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EXCAVATIONS AT SITE CA-SON-392,
NEAR PETALUMA, CALIFORNIA

by

Thomas F. King

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Contents:	Introduction
	The Site
	Excavation
	Constituents
	Cultural Features
	Artifacts and Ecofacts
	Conclusions
	Reference

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This essay originally appeared as Paper No. 16 of the Robert E. Schenk Archives of California Archaeology. It is dated June 1968 and was prepared as a research report for the Northwestern California Archaeological Society.

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INTRODUCTION

Site CA-SON-392 was first recorded by the late Lafayette Carpenter, Petaluma lawyer and amateur archaeologist, in the mid-1950s, and was brought by him to the attention of the present author, who recorded it "officially." No further work was conducted in spring, 1968, when it was decided to test the site to obtain data on two questions:

1. The characteristics and use of the unusual bedrock features.
2. The general temporal and cultural context of the site.

Since the site is not presently in danger of destruction, and since this Society is not in a position to undertake large scale pure-problem research, only a very limited program was executed at CA-SON-392.

THE SITE

CA-SON-392 comprises two loci, on the north and south banks of an east-flowing periodic stream that enters Petaluma River about 300 meters downslope from the site. The stream drops rather abruptly from a rolling hilly upland presently occupied by the Petaluma Golf and Country Club, through a broad sloping swale between hilly spurs, to mingle into the tule marsh that borders the River. Petaluma River, somewhat misnamed, is a sinuous north-reaching arm of San Francisco Bay, brackish and subject to tidal action.

The hilly flanks around CA-SON-392 are largely covered with native grasses, wild wheat, and scrub lupine. Star Thistle were noted in isolated patches among the rocks, and Bay Laurel grows along the stream. Black Oak (Quercus kelloggii) and Coast Live Oak (Quercus agrifolia), important in the Indian economy, grow in some numbers, especially along the stream banks.

The Northern Locus

The north bank of the stream is characterized by a gentle slope studded with outcrops of reddish vesicular basalt that weathers superficially to a dull gray. Into one of these outcrops, designated Feature A, six bedrock mortar cups, one anomalously large saucer-shaped depression, and twenty-three small cupules have been ground (see Figure 1). In another outcrop, downslope from Feature A, are twenty-two cupules (see Figure 2). No other outcrops seem to have been modified, and there is no evidence of structures or midden formation.

Figure 1. CA-SON-392, Feature A.

Metrical Data: Dimensions of outcrop: Dimensions of large depression: Mean dimensions of 6 mortars: Range of dimensions, 6 mortars: Mean dimensions of 23 cupules: Range of dimensions, 23 cupules:	145 x 160 cm Diam. 70 cm, depth ca. 10 cm Diam. 23.8 cm, depth 7.9 cm Diam. 15-28 cm, depth 4-12 cm Diam. 4.9 cm, depth 1.8 cm Diam. 3-11 cm, depth 1-3 cm

Figure 2. CA-SON-392, Feature B.

Metrical Data: Dimensions of outcrop: Mean dimensions of 22 cupules: Range of dimensions, 22 cupules:	105 x 100 cm Diam. 5.2 cm, depth 2.5 cm Diam. 3-10 cm, depth 1-6 cm

The Southern Locus

Directly across the stream from the modified outcrops, about 25 meters distant, is a small brown-earth midden. It lies on a surprisingly steep slope, averaging about 30 degrees, which has been subjected to massive sliding and soil creep. Limits of the midden are difficult to trace, but an approximate diameter of 30 meters is an estimate that probably approaches accuracy.

EXCAVATION

1. Northern Locus: A 1 x 3 meter unit, Unit A, was excavated to a depth of 10 cm, exposing the surroundings of the western half of Feature A. The cupule feature, Feature B, was treated similarly. The hard adobe had to be broken up with picks, but once this had been done excavation was conducted entirely by trowel, with samples forced through one-quarter inch screen as a check on recovery.

2. Southern Locus: Three 1 x 3 meter units were excavated along a N-S line down the slope of the midden, each separated from the next by 2 meters of unexcavated midden. Excavation was terminated at a depth of 20 cm, since all objectives had been met and no more time was available, though the midden may up to one meter deep. Excavation was conducted by 10 cm arbitrary contour levels, and all materials were passed through one-quarter inch screens.

CONSTITUENTS

Flakes and cores, bone and shell, and unusual rocks and other materials were retained by level. A piece count of materials recovered is presented in Table 1 below.

Table 1. Midden Constituents by Unit and Level.

Unit 1, 0-10 cm	Chert Obsidian Quartz Large Mammal Bone Small Mammal Bone Ostrea lurida Saxidomus nuttalli	5 10 0 4 0 4 1
Unit 1, 10-20 cm	Chert Obsidian Bird Bone Large Mammal Bone Small Mammal Bone Ostrea lurida Saxidomus nuttalli Protothaca staminea Tresus nuttalli Land Snail	6 9 3 4 2 4 5 1 1 3
Unit 2, 0-10 cm	Chert Obsidian Quartz Large Mammal Bone Small Mammal Bone Ostrea lurida Saxidomus nuttalli	4 7 1 3 1 10 2
Unit 2, 10-20 cm	Chert Obsidian Bird Bone Large Mammal Bone Pelvis, Medium Mammal Ostrea lurida Saxidomus nuttalli Tresus nuttalli Mytilus edulis Cancer sp.	8 10 1 4 1 8 6 4 1 3
Unit 3, 0-10 cm	Chert Obsidian Large Mammal Bone Ostrea lurida Saxidomus nuttalli Protothaca staminea Mytilus edulis	6 4 2 6 1 1 1
Unit 3, 10-20 cm	Chert Obsidian Small Mammal Bone Ostrea lurida	3 1 1 1
Unit A, 0-10 cm	Quartz Obsidian	11 1
Unit B, 0-10 cm	Chert Quartz Obsidian	16 11 4

Chert and obsidian occurred almost entirely in the form of flakes, except in Units A and B, where the preponderance of specimens were small cores. Large mammal bones were found for the most part in the form of finely splintered long bone fragments, apparently representing deer-sized ungulates.

CULTURAL FEATURES

Data on the two major surface features of CA-SON-392, the bedrock mortar and cupule outcrops, are given with their illustrations in Figures 1 and 2. In addition to these spectacular features, several other cultural constructions were located in the course of excavation, and are synopsized below.

Rock Features

Loose, patternless accumulations of fire-cracked native basalt slabs and pebbles were found in the 0-10 cm level of Unit 2 and in the 10-20 cm levels of Units 1, 2, and 3. Ash and charcoal were usually interspersed among the rocks. A very large concentration of large basalt fragments was found in Unit A curving around the west end of Feature A, but this feature may not be of human origin.

Ash Feature

A small ash lens was located at a depth of 5 cm in the southwest corner of Unit A.

Human Remains

Several fragments of human cranium, broken in antiquity, were located at an approximate depth of 4 cm in Unit 1. No other evidence of burials was encountered.

ARTIFACTS AND ECOFACTS

A complete list of artifacts and ecofacts is given below, by unit and depth. Descriptive and classificatory terminology is that in common use by central California archaeologists.

Unit A, 0-10 cm	Obsidian flake scraper; orange burned-clay sphere, 8 cm diam.
Unit B, 0-10 cm	3 obsidian flake scrapers; obsidian core; chert core end scraper; chert core
Unit 1, 5 cm	Clam (Saxidomus) disc bead
Unit 1, 10-20 cm	Clam disc bead; medial frag., bone awl
Unit 2, 0-10 cm	Complete Olivella shell, unperforated, unground, with notch at end of aperture, 8 irregular lines of punctate decoration at oblique angle to shell axis, near callous (Figure 3d)
Unit 2, 5-10 cm	Gray steatite "plug" cylinder 12 x 8 mm (Figure 3c); chert core
Unit 2, 10 cm	Pointed obsidian flake scraper; clam disc bead fragment
Unit 2, 10-20 cm	Carbonized probable pinenut
Unit 2, 17 cm	Base of serrated, non-barbed point, stemmed (Figure 3b)
Unit 3, 3 cm	Worked obsidian
Unit 3, 5 cm	Obsidian bipoint; medial fragment, bone awl (2)
Unit 3, 10 cm	Thin-lipped (3a1) Olivella bead
Miscellaneous	Fist-sized quartz core, possibly modified as core tool -- streambed. Clam disc bead; base, obsidian bipoint; obsidian corner-notched point 40 x 18 x 6 mm (Figure 3a) -- talus from badger burrow, ca 10' (3 m) NW of Unit 2.

Figure 3. CA-SON-392 Artifacts. A. Corner-notched point. B. Serrated, non-barbed point. C. Steatite "Plug." D. Incised Olivella shell. E. Clam disc bead. F. Olivella thin-lipped bead.

CONCLUSIONS

The excavations conducted at CA-SON-392 were intended to be probing, not definitive, and it would be inappropriate to draw hard conclusions here. It should be noted, however, that the excavations have indicated that the site is unusual in several respects:

• Feature A is substantially unique in the Coast Miwok ethnosphere. A mortar (bedrock) feature has been reported on Walker Creek in Marin County (David Craig, personal communication) but apparently it does not possess the very broad, shallow grinding basin or the associated cupules.

• Feature B is also very unusual within the Coast Miwok ethnic boundaries. Similar stones are found to the north in Pomo territory, where they are ethnographically associated with fertility and possibly rain-making ritual techniques (Heizer 1953). A stone with cupules has recently been located in the Pomo/Coast Miwok borderland between Cotati and Santa Rosa (David Fredrickson, personal communication) but its ethnic affiliation is difficult to suggest.

• While the pre-contact ecology of the Petaluma River is imperfectly known, certain shellfish frequencies found in the CA-SON-392 midden seem out of place in this habitat (e.g., Saxidomus, Tresus) while locally abundant species (e.g., M. edulis) are comparatively rare in the site. The apparent pinenut found in Unit 2 constitutes another anomaly, since pine trees today are not found closer than the Marin Highlands, over 5 miles away.

• It is curious that no pestles were found around the bedrock mortar outcrop or elsewhere in the site, and that scrapers and cores were abundant in Unit B. Certain other artifacts, for instance the incised Olivella shell and the steatite plug, are unusual, but with such a small sample recovered it would be dangerous to draw conclusions.

In conclusion, it may be stated that CA-SON-392 is worthy of much more intensive, careful investigation, especially should it become threatened with destruction as the City of Petaluma expands southward.

REFERENCE
Heizer, R.F. 1953. Sacred Rain Rocks of Northern California. Reports of the University of California Archaeological Survey 20:33-38.