eee p p petrogletrogletroglyphyphyph b b …

53GENERAL SESSIONS 1, 2, AND 4 AND SYMPOSIUM 3: THEORETICAL CONTRIBUTIONS, ROCK ART, THE ETHNOGRAPHIC LAYER, AND NORTHERN CALIFORNIA

Kathy O’Brien, California State University, HaywardDonna Gil let te, University of Cali fornia, Berkeley

Roger Kelly, Adjunct Professor (2003), Cali fornia State University, Hayward

Proceedings of the Society for Cali fornia Archaeology, Volume 18, 2005, pp 53-64

EEEEEXCAXCAXCAXCAXCAVVVVVAAAAATIONTIONTIONTIONTION AAAAATTTTT AAAAA P P P P PETROGLETROGLETROGLETROGLETROGLYPHYPHYPHYPHYPH B B B B BOULDEROULDEROULDEROULDEROULDER: C: C: C: C: CANYONANYONANYONANYONANYON T T T T TRAILRAILRAILRAILRAIL P P P P PARKARKARKARKARK, CA-CCO-152, CA-CCO-152, CA-CCO-152, CA-CCO-152, CA-CCO-152

KATHY O’BRIEN, DONNA GILLETTE, AND ROGER KELLY

Excavation in a rock-art context has received little consideration. A boulder in a sandy playground in Canyon Trail Park in El Cerrito,Contra Costa County, containing abstract elements including PCNs, cupules, and grooves, provided an opportunity for such a study.The city has accepted a proposal to renovate the site from a sandy playground to a Native American Interpretive Park. In preparationfor the implementation, Cal State University, Hayward, Anthropology Department and the Bay Area Rock Art Research Association(BARARA) collaborated on an excavation/recording field school to further investigate and document the cultural prehistory of the site.

CA-CCO-152 is a rock art site located in CanyonTrail Park, a city park in the East Bay city of ElCerrito in the San Francisco Bay Area (Figure

1). Pilling and Meighan first recorded the site onOctober 26, 1949. Squire filed an ArchaeologicalFeature Record on October 30, 1949, detailing the rockart features on the chlorite schist boulder (which hemisidentified as steatite). The most prominent featureson the boulder are cupules and pecked curvilinearnucleated petroglyphs (PCNs).

The goals of the project were to recover (1) datapertaining to the rock art elements on the boulder andmap the surface; (2) any artifacts related to prehistoric orhistoric (modern) human activity at the site; and (3)natural materials such as shell, charcoal, or plant remainsfrom occupation levels associated with humanmodification of the boulder – to date the culturalactivities at the site. The team hoped to encounterartifacts such as stone tools, projectile points, charcoalor fire-altered rocks, bones, shells of clams or othershellfish, and plant remains. Recording a detailedstratigraphy of the soil at the site was included in theplans, to aid in both interpreting the site and planningfuture preservations and conservation activities.Results of fieldwork toward these goals are discussedbelow.

The project was to provide previously unavailabledata about both the boulder and its surroundings.Excavations on the eastern side of the boulderdetermined that the petroglyphs extend well belowmodern ground level to a depth of at least 40 cm, andperhaps deeper.

Figure 1: Archaeological sites in the immediate SanFrancisco Bay Area. Location of Canyon Trail Park,CA-CCo-152, indicated by arrow (from Moratto 1984).

54 PROCEEDINGS OF THE SOCIETY FOR CALIFORNIA ARCHAEOLOGY, VOL. 18, 2005

PROJECT BACKGROUND

Natural Setting

CA-CCO-152 is located at an elevation ofapproximately 200 feet in the East Bay Hills,overlooking San Francisco Bay, Angel Island, and theGolden Gate. The boulder where the petroglyphelements occur is now located in a playground, whichwas constructed during 1966-67 after a local resident,Stella Anderson, brought the cultural significance of theboulder to the attention of the city council (BerkeleyGazette, June 24, 1953). The site was altered duringconstruction of the playground. An area around theboulder was leveled and sand brought in to create a playarea. This environment has resulted in considerabledamage to the features on the boulder due to abrasion ofthe sand and children playing on it (Daniels 1999).

The area immediately around the playground iscovered with non-native ivy. Coast live oaks (Quercusagrifolia) grow on the slope south of the boulder.Redwoods (Sequoia sempervirens), although native to theregion, were planted when the park was established.Little remains of the environment that existed whenthe petroglyph elements were placed on the boulder.One aspect of the site still largely intact is themagnificent view it affords of the Bay. Researches havenoted the probable link between sites chosen byancient people for petroglyphs, particularly the PCNstyle noted on this boulder, and the natural features ofthe locale, including the view-shed (Fentress 1999;Miller 1977).

The site is within the Baxter Creek watershed, andrecent attempts to rejuvenate the Pacific chorus frog(Pseudacris regil la) population have met withconsiderable success. The park is now home to thelargest known breeding population of the species (JimMcKissock, personal communication, 2004) in the EastBay. This work has restored the small pond locatedwithin a few meters of the boulder. Native flora hasbeen reintroduced to the pond area, and the long-termgoal is to replace the non-native ivy on the northern andwestern slopes with native flora.

The slope to the southeast of the boulder is anatural terrain undisturbed by modern development.Native flora including soaproot (Chlorogalumpomeridianum), grasses, and edible roots (Brodiaea)continue to flourish in this location. The density of thesoaproot exceeds that normally encountered and couldindicate that the hillside was tended by the indigenouspopulation to encourage growth of this important plant(Jim McKissock, personal communication, 2004).Research indicates that indigenous peoples protected

resources and promoted production of desired flora(Levy 1978:491; Margolin 1978:49; Moratto 1984:3).

The pipevine swallowtail butterfly (Battusphilenor), a rare species, has been observed on thehillside. During the caterpillar stage, this speciesconsumes the leaves of the Dutchman’s or Californiapipeline (Aristolochia californica), a native climbingvine found on the natural slope (Jim McKissock,personal communication, 2004). The preservation ofthe existing natural slope and the restoration of furthernon-native flora on the remainder of the slope wouldprotect the habitat of these two species and furtherenhance the location as the site of an interpretive centerfor the study of local flora, fauna, and early humanhabitation.

The area around the park consists of neighborhoodsconstructed from the late 1940s to the 1970s. A steep,paved trail leads east, up the canyon, to the remainderof the park, which lies along Gatto Street. Access to thelower portion of the park where the boulder is located isalong a residential street (Conlon Ave) and is markedby a weathered sign set back from the street. Benchesare available, but no picnicking or barbequing facilitiesare situated near the boulder. Present usage of the lowerpark consists mainly of people passing by, walking theirdogs or simply going for a stroll along the paved trail.The play area is largely in disuse, and the equipment isold.

Archaeological Research

The investigation of CCO-152 is only the secondknown excavation at a Bay Area rock art site, and thefindings must be viewed within the broader context ofSan Francisco Bay Area prehistory. Archaeologicalsurvey and excavation in the immediate vicinity ofCanyon Trail Park is extremely limited. Although thesite was reported in 1949, it has only recently beenmentioned in the literature. Hotz-Steenhoven (1986)discussed the petroglyphs and reported that a neighborrecalls a midden upstream, but it was no longer inexistence when she visited the site and was notrecorded at the Northwest Information Center atSonoma State University. Fentress (1992) mentions theboulder as a rock art site and corrects the lithographyfrom steatite to chlorite schist. Gillette (1998) includesCA-CCO-152 in her survey of PCN sites. Daniels (1999)completed an extensive survey of the petroglyphelements on the boulder and reports that there are atleast 188 cupules, 11 PCNs, and eight bedrock mortars.Thus, it is only within the last two decades that the sitehas received recognition as part of an important andlittle-understood rock art tradition in central Californiaand beyond.


Schist, reported variously as green or blue, isabundant in Wildcat Canyon. Heizer and Treganza(1944:338), citing Loud (1924), report that “near themouth of Wildcat Canyon in the stream bed aregreenstone schist boulders, some of them very large.Nearby shellmounds in the vicinity of Richmond andBerkeley yield numerous artifacts made of thismaterial, and there seems little doubt that the WildcatCanyon float material was the source.” Loud (1924:336-337) postulated, “the larger Stege mound was amanufacturing site for implements of greenstone schist.It is probable that the inhabitants got their materialfrom the mouth of Wildcat cañon, three miles distant…”

A cultural connection between the habitations atthe nearby mounds (the Stege mounds are only twomiles from CA-CCO-152) and the markings on theboulder is accepted by many researchers. Daniels(1999) speculates on the ritual or sacred nature of thesite, although the connection between the localinhabitants encountered by the first Europeans in theregion and petroglyph sites is not documented for theimmediate Bay Area. Farther north, ethnographicaccounts of Pomo baby-rock rituals were recorded intothe twentieth century (Loeb 1926; Barrett 1952).

Ethnographic Research

Records kept by the Spanish and ethnographicaccounts gathered in the nineteenth and twentiethcenturies allow archaeologists to reconstruct with somecertainty the areas in which various languages werespoken in Central California at the time of contact. Amap drawn from this data (Figure 2A) indicates that CA-CCO-152 was in territory occupied by speakers ofCostanoan (Ohlone), but that contact with Coast Miwok,Bay Miwok and Patwin speakers would not have beendifficult.

We know from both archaeological andethnographic data (Fagan 2003, Kroeber 1925, Levy1978, among others) that native peoples’ social andpolitical structure was organized around whatarchaeologists refer to as a triblet, an independentorganization that rarely exceeded a few hundredpersons. Each triblet had distinct territory and resources,and the people moved from one resource location to thenext in seasonal cycles to exploit the abundantresources of the Bay Area. CA-CCO-152 lies within aregion that was occupied at the time of Spanish contactby people speaking languages in the Penutian family.The region stretching from Point Sur to the SanFrancisco Bay Area was home to about 10,000 peoplewho spoke eight to 12 related languages and wereorganized into triblets of about 250 people. TheHuchiun occupied an area in the East Bay along San

Francisco and San Pablo bays from the cities of SanPablo and Richmond extending south to NorthOakland, perhaps encompassing Emeryville, and eastthrough the East Bay Hills (Figure 2B). Their territoryabutted that of the Bay Miwok, another group speakinglanguages in the Penutian family. Unfortunately, thereare no known direct descendents of the Huchiun triblet,but an increasing number of descendents trace theirconnections to several of the other Costanoan/Ohlonetribelets, as well as the Bay Miwok.

What, if any, cultural affiliation these nativepeoples have with the petroglyph boulder has not beenestablished. There are no ethnographic accounts of theCostanoan (Ohlone) creating cupules or PCNs. The factthat the boulder was located within Huchiun territory atthe time of European arrival does not demonstrate thatthe Huchiun created the markings. The cupules andPCNs could be the work of ancient peoples for whomwe have no ethnographic evidence.

Rock Art

Although rock art recording in North America beganin the nineteenth century, rock art research in centralCalifornia is a relatively new area of investigation.Clewlow (1978:620), in an article for the Handbook ofNorth American Indians, Volume 8, California, notedthat “no rock art data are on record for Alameda,…Marin,[19 counties are listed]” and includes Contra Costaamong four counties which “have so few sites that theyare not amenable to stylistic discussion.” This situationhas been altered radically in the subsequent twodecades. The following paragraph summarizes thesedevelopments – though it does not present anexhaustive summary of rock art research in the BayArea.

In 1974, Hotz (now Hotz-Steenhoven) andClewlow published a brief article reporting the firstknown petroglyphs in Marin County. They reported “aseries of 90-95 incisions or scratches of elliptical or ovalshape” (Hotz and Clewlow 1974:149), and furtherspeculated that other sites existed in Marin County thathad gone unrecognized. In 1977, Miller (now Saltzman)identified no fewer than 68 rocks with petroglyphs inthe North Coast Ranges of California. Subsequentresearch included two master’s theses presented toCalifornia State University, Hayward (Fentress 1992and Gillette 1998) that specifically identified CA-CCO-152 as a petroglyph site. Daniels (1999) mapped theboulder, summarized the elements visible above theground surface, and speculated on social activity at rockart sites in a paper presented at the California IndianConference in 1999.


Figure 2: (A) Languages/Tribal areas of the San Francisco Bay Area, and (B) tribelet areas as determined frommission records (from Milliken 1995). Canyon Trail Park, CA-CCo-152, is indicated by the arrow.

A. B.

Various researchers (Daniels 1999; Fentress 1992;Gillette 1998; Hotz-Steenhoven 1986) have reportedon the petroglyph boulder in Canyon Trail Park. Allagree that it contains cupules; pecked, curvilinear,nucleated (PCN) elements; and straight grooves. Theidentification of several of the elements as bedrockmortars (Squire 1949, Fentress1992, and Daniels 1999)seems less certain. Hotz-Steenhoven (1986:181) refersto these elements as “deeply worn conical shapes thatseem to be mortars” and “mortar-like holes,” indicatingsome uncertainty. No evidence of food preparation,which would substantiate the use of the holes as mortars,has been found at the site. Other possible uses for thefeatures should be considered.

Heizer and Clewlow (1973) segregated Californiarock art into five element categories. The ‘human’ and‘animal’ categories were representational, while the‘circle and dot,’ ‘angular,’ and ‘curvilinear’ categorieswere assigned to elements that the researchers couldnot recognize as a representation, however stylized, of ahuman or animal. Rock art researchers have providedspecific names for particular elements. Cupules aresmall, circular or oval indentations in a rock created byhumans (not the result of geological or otherenvironmental factors). Larger depressions used forfood preparation are referred to as bedrock mortars(BRMs). As noted by Fentress (1994:70), “the two formsactually represent opposite ends of a size continuumranging from ca. 2 cm to ca. 20 cm in diameter. At either

end of the scale the forms are obviously different;however, in the middle of the range it is often difficultto tell where a cupule ends and a BRM starts.” Miller(1977:44) provided the basic definition for peckedcurvilinear nucleated (PCN) elements: the basicelements are circles and ovals, which have nuclei, thatappear raised. They seldom occur in any discernablepattern. The elements are pecked into the surface ofthe rock (generally a chlorite schist boulder). The sizeranges from 5-15 cm in diameter (exteriormeasurements), with the nuclei from 2.5-20.5 cm indiameter. The depth of the pecking and the width varyfrom 0.5-0.6 cm.

Previous researchers noted “PCN-like” circular oroval grooves, horse hoof-print shaped, or similarlydescribed elements in petroglyphs in central Californiaprior to Miller’s definition of the style. Julian H.Steward, in his 1929 work, Petroglyphs of California andAdjoining States, noted their presence in a number ofsites. A site in the southwest corner of Trinity Countywas identified as having “circles and curves.” Anothernear Willits was described as having “’horse tracks’ andIndian signs,” while still another near Porter Creek inSonoma County near Healdsburg was described ashaving petroglyphs “generally oblong circles or ovals,some of which contain crosses.”

Hotz-Steenhoven (1986) noted that many PCNscould be identified from site recordings where the


elements are not mentioned, particularly whenphotographs of the petroglyphs are included in the siterecord. She references two Mendicino sites (recordedby Samuel A. Barrett in 1953) where “closeexamination of Barrett’s photographs of the two sitesbrings to light these oval or circular forms with groovesand cups seemingly superimposed on them” (Hotz-Steenhoven 1986:178). Her visit to the site confirmedthe presence of PCNs on the boulders.

The superposition of various petroglyph elementson PCNs is a recurring phenomenon, which leads to theconclusion by various researchers (Gillette 1998, 2003;Miller 1977; Parkman 1993) that PCNs are ofconsiderable antiquity. Nowhere in the research is therea recorded instance of a PCN superimposed on anotherelement such as a cupule, while numerous instances ofthe reverse position have been reported. However, theCanyon Trail Park boulder does not have cupulessuperimposed on the PCNs.

FIELDWORK RESULTS AND METHODS

Site Description

In their original recording of CA-CCO-152, Pillingsand Meighan (1949) identified four petroglyph rocks.The boulder investigated during this excavation isapparently Feature 1 in the original site report. Feature2 was located northwest of this boulder (directlybetween Feature 1 and the intersection of Fern andCedar Streets), while Features 3 and 4 were located tothe west of Cedar Street (but south of the intersectionwith Fern Street).

Extensive modification hasoccurred to the site in the modernera, particularly since it was firstrecorded. The petroglyph boulderis now located in a small children’splay area. The site has beenleveled and backfilled with sand,and play structures have beeninstalled in poured concrete. Noprehistoric artifacts exist on thismodified surface area, althoughlocal residents frequentlyencounter artifacts within a one-half-mile radius of the site (LarryDamon, personal communication2003).

Squire (1949) reportedFeature 1 of CCO-152 asmeasuring “10’ 10” [3.3 meters]

north-south, 11’6” [3.5 meters] E-W” and “2 to 3 ft. [0.6to 0.9 meters] above the surface of the ground.”Modifications to the site have resulted in a present-dayposition above the ground of three to four feet,indicating that the ground level has been lowered inrecent decades. However, the site report does disputethe claim by a “long-time resident” who reported, “therock was once almost covered by soil” (Hotz-Steenhoven 1986:182). Local residents told theexcavation crew that the boulder was moved from alocation up the canyon at the time the park wasconstructed (Leon McNeeley and Larry Damon,personal communication 2003), an argument notsubstantiated by either the 1953 Berkeley Gazettearticle regarding the creation of the park, nor the presentcondition of the boulder.

Efforts to locate the other three features in theoriginal site report were unsuccessful. Several attemptswere made to contact the property owner on CedarStreet where the site sketch indicates Features 3 and 4are located, but no one answered the door. DonnaGillette (personal communication, 2003) saw at leastone of the two features in the mid-1990s in a backyard,which was confirmed in June 2004. The limits of thesite for this study were established as the boulder and itsimmediate surroundings as shown in Figure 3.

The geology of the site is complicated, and only asummary is possible here. Western California isdominated by the San Andreas Fault system, which isthe result of the movement between the North Americaand Pacific plates as the latter moves northwest. Theearth in the region—the rocks, minerals, and soils—is

Figure 3: Photograph of Canyon Trail Park with petroglyph boulder at center.

K. O’Brien


the result of further tectonic forces. The“heterogeneous assemblage of greywacke, shale,altered volcanic rocks, chert, limestone, and peculiarmetamorphic rocks” (Bailey et al. 1964:11) is referredto as the Franciscan Assemblage. It is the result of thesubduction (movement of a portion of the earth’soceanic crust toward the core which results in increasedtemperature and pressure) of an ancient oceanic plateand the subsequent movement of the metamorphedmaterials as the Coastal Ranges thrust upward. CA-CCO-152 lies just west of the Hayward Fault, an activefault extending through the East Bay Hills. The portionof the Franciscan Assemblage to the west of theHayward Fault is believed to have been formed late inthe Cretaceous Period (144 to 65 million years ago)(Bailey et al. 1964).

The boulder lies in a steep ravine, probably buriedat one time by a meter or two of alluvial deposits, theupper layers of which have been disturbed in recenttimes. The matrix surrounding the boulder andunderlying the 1960s park construction materials is alocal dense, dark clayey deposit. Nearness to a flowingstream may have resulted in episodic alluvium layersaround the boulder, but no distinguishable layering wasapparent. There were very few small, water-wornpebbles or silts, but some of the schist pieces appearedto be rounded by movement. Cristina Castanha,geologist and Ph.D. candidate at the University ofCalifornia, Berkeley, visited the site on June 7, 2003and commented that the soil is “almost certainly ClearLake Clay (but plausibly Cropley Clay) – both vertisolscharacterized by monmorillonite clays”(personalcommunication, June 10, 2003). Determining the ageof these soils is difficult. Castanha noted that the soilscould be several thousand years old if formed fromsandstone, or as young as several hundred years ifformed from shale. Her comments indicate that sheconsulted the geologic map for the RichmondQuadrangle (Thomas Dibble 1980) and that “the sideof the creek where the boulder is is mapped asFranciscan greenstone, ‘commonly altered to softchloritic material and highly weathered’” (personalcommunication, 6/10/2003).

As noted, the boulder has been identified aschlorite schist (Fentress 1992:97). Chlorite schist is ametamorphic rock, which began as shale, a sedimentaryrock consisting of clay minerals, and was subjected tolow- to intermediate-grade metamorphosis (Skinnerand Porter 1987:138). Schists are identified by theircoarse-grained texture and tendency to foliate intoplaty fragments. Chlorite is “a family of sheet silicateminerals, containing magnesium, iron, and aluminum,formed under low-temperature and, generally, low-

pressure metamorphic conditions. Chlorite is usuallygreen and has one perfect cleavage” (Wahrhaftig 1984).

Fieldwork Strategy and Methods

As noted in the introduction, the fieldwork had threeprimary goals:

• To recover data pertaining to the rock artelements on the boulder and map the surface.The current location of the boulder within theconfines of a playground has contributed to theerosion of the petroglyph elements due toabrasion caused by children with sandy or grittyshoes, hands, etc., playing on the surface of therock. A detailed recording of the elementswould help preserve the data for future research.

• To excavate artifacts related to prehistoric orhistoric (modern) human activity at the site. Itwas hoped that such artifacts, if they wereencountered, would assist in building anaccurate picture of activities at the site. Thepresence of food remains, evidence of food-preparation or gathering activities, lithics suchas projectile points, or other artifacts, would helpin placing the site within the prehistory of theBay Area.

• To recover materials for use in dating the humanactivities at the site. Dating petroglyph sitescontinues to be challenging. Any firmassociation between an artifact that could bedated (for example, a piece of charcoal thatcould be dated using radiocarbon chemistry) andthe creation of petroglyphs would be asignificant contribution to knowledge.

A further objective was to gain an understanding ofthe stratigraphy of the site, particularly as it relates tohow the locale has changed in the last 10,000 years.Since initial human occupation of central Californiapresumably occurred within this period, understandingthe geological changes during that time will help toassess the site’s appeal to the people who made thepetroglyphs.

A grid was established around the boulder (Figure4) and the site and present structure mapped using aplane table, alidade, and stadia rod. The site datum wasestablished in the eastern corner of the playground andthe site baseline extended across the playground at abearing of 800 W of magnetic N. A grid was establishedat 900 angles from the baseline. Due to obstructions(concrete, playground equipment), an irregular grid


with lines perpendicular to the baseline at 5, 8, 11, 14,14, 17, 24, and 29 meters from the site datum wasestablished. Units were measured off of these lines.Units were not square because it was necessary toextend or contract them around the petroglyph boulder.

The four units encircling the boulder wereexcavated in 20-cm levels. The soil was remarkablyconsistent throughout the site. Cement wasencountered in units located near the boulder. It wasapparently poured during construction of the park andwas observed at depths ranging from 2 cm to 16 cm.Some cement was removed to aid in digging, but manyslabs were extensive and could not be removed withhand tools. Excavations to a depth of 67 cm indicatedno significant variations in the soil (no visiblestratigraphic features), and use of an auger gave similarresults, although some possible variation was noted at adepth of 150 cm, where the character of the soil changedfrom dark brown to brown. Rock of unknowncomposition halted the auger at 180 cm. Thus, no sitestratigraphy was established and no occupation levelsencountered during the excavations.

Several shovel test units (STUs) were placed on thewestern portion of the playground to gain anunderstanding of the extent of the alluvial deposit. Thedata gained from STUs around the climbing structureindicated that concrete slabs were poured around thesupports to a depth of at least 25 cm. The surroundingsoil is an undifferentiated, dense sandy clay with littleor no organic matter. An STU near the north retainingwall encountered a similar soil matrix. How much of thesoil was removed prior to leveling the area and bringingin sand for the playground could not be determined.

Collection procedures utilized ¼ inch screens forexcavation units and shovel test units. Excavatedmaterials were difficult to screen due to the clayey

nature of the earth, which clumped in clodsof various size. Students were giveninstructions to examine and recover mostrocks in the clay mixture. They weremonitored as they hand-excavated, shoveledmaterials to screens, and processed thematrix. Collected materials were placed inbags that were labeled with site, unit, level,date and collector(s). A student was assignedto maintain a field catalog. Each item wasbriefly examined, dry-brushed and measuredfor gross size and a brief description enteredin the field catalog.

At the conclusion of the fieldwork, RogerKelly examined the assemblage. Each provenience

bag was sorted by lithology and size seriation followedby visual examination. Procedures included closeinspection with 10x and 20x hand-lenses under strongillumination to reveal markings that could possibly bethe result of cultural modification.

FINDINGS

Significant progress was made toward project goals.BARARA members, and Christine Gralapp in particular,painstakingly mapped the cultural markings on theboulder, including those revealed below the modernground surface. Numerous photos, both 35mm anddigital, were taken and remain in the BARARA archivesfor future researchers to access. The archaeologystudents collected nearly 800 items from the excavatedsoils. Most of these items (over 90%) were unmodifiedor natural rocks, but over a dozen have wear marksdiffering from the rest of the assemblage. Artifacts fromthe historic/modern era (glass, plastic, and metal), whichare most likely from the decades the site served as aplayground, were also collected. Unfortunately, theassociation of the items collected with the petroglyphson the boulder is unlikely. The identification of the soilas an alluvial deposit, along with the presence ofcultural markings below the modern ground surface,leads to the conclusion that items located within theexcavated soils could not have been at the site whennative people created the markings. Excavations didnot reveal any charcoal or other material that could bedated, so the team was not able to determine a date forthe petroglyphs (not even a relative date can bepostulated at this time). No complete or fragmentarytools of stone, bone, antler, or other material wererecovered.

Details of the findings are in the following twosections of this report.

Figure 4: Diagram of the site overlay on a diagram of the parkconstruction. Datum line is 29 meters (diagram R. Kelly).


Petroglyph Boulder

Daniels (1999) completed a thorough examinationof the cultural markings on the boulder; thus, thedimensions and depth of each marking were notrecorded for the present study. Gralapp, BARARAmember and a skilled medical illustrator, prepared thedrawings in Figure 5. While the drawings serve toillustrate the features currently visible on the boulder,consistent measuring of dimensions and depth overtime are the only certain means of monitoring theeffects of erosion and other detrimental forces on thepetroglyphs.

As mentioned above, cultural markings below thepresent ground surface were found only on the east sideof the boulder. As indicated by the line in Figure 5B, 26cupules were uncovered in the excavation. If the soil isalluvial deposit, then it seems likely that the markingshave been buried for centuries, if not millennia. Datingthe alluvial deposit by would provide the most recentpossible date for the cultural markings, because theypredate the soil deposition.

Artifact Assemblage

In total, 776 items were catalogued from theexcavation units and the shovel test units. No obsidian,charcoal, invertebrate shell (fresh or marine), bone, orfire-cracked rock were observed in any unit.Approximately 50 historic/modern artifacts—glass,nails, plastic, concrete, ceramic, and a marble—wererecovered. These itemsare not associated withprehistoric use of the siteand were not analyzed indetail. The remainder ofthe assemblage is lithic(rocks) and will bediscussed in greater depth.

Lithics

Almost all of the lithicmaterial—over 700items—are schist, probablyactinolite schist, which isdefined as fine- tomedium-grained, ‘green,’and well foliated (that is,with flat or wavy parallelplanes which separatealong lamellar or tabularjoints), containing visiblemica and chlorite flakes.Actinolite is a mineral that

gives the dark green hue to the metamorphic schist.Glaucophane is another mineral found in schists but it isvery fine-grained, rarely foliated, and of blue or violethues. There were also several Franciscan mudstoneitems—metamorphized sandstones—that arecommonly associated with schist sources.

The assemblage of schist pieces is composed oftwo major types: small to very large, blocky, angular,and irregular natural pieces, sometimes with reddish/orange inclusions; and flattish, tabular, thin, and oftentriangular or polygonal small pieces. Many piecesreflected mica when handled and appeared to be flakesnaturally split from larger pieces. However, 16 of thesmall, tabular pieces appear to be modified in a mannernot observed for the other flakes. This group of piecesappeared to have been subjected to a grinding/rubbingmotion, leaving the edges a lighter, contrasting color,usually along convex-curved edges. Several modifiedpieces are similar in appearance (at least as discerniblefrom the photographs in the report) to the worked piecesreported by Fentress (1999) and illustrated in his Plates3 a and b, 4 a and c, and 6 a, b, and c. The units, depths,and dimensions of the flakes identified as possiblyworked or modified appear in Table 1.

The identification of the stones as possibly havingbeen modified raises interesting issues forinterpretation of excavation results. If the stones havebeen modified, and further research with the aid of alithics expert is necessary to confirm this, then thequestion arises, who used these tools and when? A

Table 1: Data for possibly “modified” rocks. NA - Data not available or not recorded.

.oN tinU *htpeDthgieW

)mg(htgneL

)mc(htdiW)mc(

ssenkcihT)mc( tnemmoC

1 7 AN 1.95 9.3 5.3 6.2

2 3 04-02 0.01 9.2 3.2 1.1

3 3 04-02 6.22 3.6 8.3 8.0

4 3 04-02 6.27 4.7 9.4 6.1

5 1 AN 9.5 8.3 1.1 9.0

6 2 53-0 0.9 0.3 6.1 1.1

7 7 02-0 2.8 9.3 7.2 6.0 .seceipowtwoN

8 4 02-0 0.23 6.4 1.3 3.2

9 4 02-0 2.83 5.4 7.2 1.2

01 4 +04 7.12 7.7 2.3 6.0

11 2UTS 02-0 4.21 6.3 1.2 2.1

21 6&5 76-0 3.41 2.5 2.2 0.1

31 AN AN 8.2 2.3 4.1 5.0

41 2 04-02 7.2921 32 7 0.4 egdexevnocgnolaraewfomc5

51 7&2 03-0 6.91 0.7 7.2 3.1

61 7&2 02-0 3.5 2.3 3.1 8.0


Figure 5: (A) Drawing of petroglyphs discernible on theboulder as of 2003, overhead perspective; (B): Drawing ofpetroglyphs on east side of boulder. Twenty-six cupules wereuncovered below ground level (drawings by C. Gralapp).

A.

B.


better understanding of the alluvial deposit is necessaryto clarify the deposition of the soil and thus therelationship of the items recovered from it to theboulder. These questions, and others, are beingaddressed in continuing research at the site.

CONCLUSIONS

The presence of cupules and PCNs on the exposedsurface of the boulder indicates that the site is of ritualimportance to native people. The investigation at CA-CCO-152 (Canyon Trail Park) demonstrates that thecultural markings continue below present ground levelto a depth in excess of 40 cm. Further research isnecessary to determine where the ground surface was(at what depth) when the elements were placed on theboulder. The determination of a date for the placementof the cupules and PCNs is not possible from the datacollected during June 2003. The proposed antiquity ofthe PCNs does not preclude several periods of use andreuse of the boulder by people inhabiting the Bay Areaover many centuries. The origin of the site with regardto both time and ethnographic data remains anunanswered question. Comparison of newly revealedelements to those on the exposed surface of the boulderis not possible due to the erosion above the presentground surface.

In conclusion, native people visited the site forreligious and spiritual purposes. The boulder must beconsidered within the natural and cultural landscape.The imposing views of Angel Island, Mt. Tamalpias,and the Golden Gate no doubt attracted people to thesite. The large number of markings on the boulderclearly indicates that CA-CCO-152 was well known and

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revered by the native people of the Bay Area.

Acknowledgments

This report presents the archaeological investigationsconducted at CA-CCO-152 in May and June of 2003. LeighMarymor, Co-Chairperson of the Bay Area Rock Art ResearchAssociation (BARARA), served as the catalyst for theexcavation and the Plan for Conservation and Protection of theCanyon Trail Petroglyph Rock and its Environment. Theexcavation took place with the cooperation of many people andgroups. The Anthropology Department at California StateUniversity, Hayward (CSUH), with BARARA, conducted the workunder the auspices of the City of El Cerrito, California. RogerKelly, Adjunct Professor at CSUH and instructor for the field-methods course, was the site lead. The CSUH team includedChimalpahin Arce, Kathleen Bencik, Lori Clanton, CarmenCuellar, Katherine Fox, Ivah Gentilini, Jason Hahn, RubenJimenez, Abrahm Jones, Marianne Klinkowski, ElizabethMoore, Laura Pellaton, Heidi Schmitt, Jami Shaw, Pauline Stahl,Lucretia Whitener and Kathy O’Brien (Department ofAnthropology graduate student assistant); while the BARARA

group included Donna Gillette, Christine Gralapp, LeighMarymor, Richard Swartz, Paul Freeman, Teresa Saltzman,Rentia Ouzman, Arthur Monroe, and others. The Friends ofBaxter Creek also played an ongoing role supporting both theresearch and conservation of the petroglyph boulder.The location of the excavation in a city park provided a highlevel of visibility to the work and encouraged neighborhoodinvolvement. The excavation team provided a table with generalinformation on archaeology as well as site-specific information,an especially appropriate activity given that May is CaliforniaArchaeology Month. The local press provided coverage, andneighbors stopped by to provide history of the area. Manypeople offered their assistance, and several were put to work onthe spot, including youngsters. Attempts were made to notify thelocal Native community, but members were unable to attend theexcavation. Prof. Beverly Ortiz (CSUH) visited the site andprovided a brief lecture on the Costanoan (Ohlone) to thestudents from CSUH.

We would especially like to thank the City of El Cerrito, and inparticular the members of the City Council and RecreationCommission, and Monica Kortz, Director of the RecreationDepartment, for their approval and unflagging support of thisproject.

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