Mammoth Rub Update - Society for California Archaeology

A similar coastal and interior pasture system likely existed
south of the California River as well. A grassland (or grassland
savanna) of approximately 300,000 ha probably existed
beneath the current San Francisco Bay and southward to San
Juan Bautista. To the west, an approximately 400,000-ha prairie
extended from the mouth of the California River south to the
San Benito River. “Franciscan Valley” is what Daniel Axelrod
(1981:848) has termed the trough that is now inundated by San
Francisco Bay. For the purposes of my discussion, I use the
term “Franciscan Valley” to designate the area extending from
Cloverdale south to San Juan Bautista. Likewise, my “Farallon
Plain” extends from a point north of the Russian River’s mouth
south to the San Benito River. Thus, the Franciscan Valley of
the late Pleistocene measured approximately 500,000 ha while
the Farallon Plain was at least 700,000 ha is size. At 1.2 million
ha, the combined Farallon Plain–Franciscan Valley ecosystem
was approximately 1/8 the size of today’s Serengeti-Mara
ecosystem in East Africa. 7
A number of obvious east-west corridors linked these
interior and coastal “pastures,” allowing for the easy
anastrophic migration movements of herds of megaherbivores
(cf. Jefferson 1988; Jefferson and Goldin 1989). 8 The
Mammoth Rocks site sits adjacent to one such corridor, the
lower Russian River Valley. Another corridor was probably the
area comprised of the Estero Americano, Estero San Antonio,
San Antonio Creek, Americano Creek, and Stemple Creek
drainage systems linking Novato and Petaluma with Bodega
Bay. Further south, another corridor most likely followed the
Crystal Springs Reservoir (San Andreas Fault) linking Palo Alto
with San Francisco’s Lake Merced area.
Naturally, the most obvious corridor connecting the
Franciscan Valley with the Farallon Plain followed the south
side of the California River through the Golden Gate. During
the late Pleistocene, this corridor passed through what I term
the “Alcatraz Triangle,” an area located just inside the Golden
Gate and bounded by the Golden Gate, Angel Island, and
Alcatraz Island. One area of interest within the Triangle is
revealed by bathymetric data. Near the Triangle’s center are
found three rock pinnacles known as Harding, Shag, and Arch
Rocks. 9 All three are currently hidden beneath the waters of
San Francisco Bay. However, during the late Pleistocene, all
three rocks were exposed. Harding Rock, the largest of the
three, stood over 100 m in height. 10 This trio of rocks
commanded an area where the trail corridor narrowed down as
it approached the Golden Gate. Such an area would have
provided ideal cover for Ice Age predators (especially Smilodon
californicus, Panthera leo, and Arctous simus) intent on ambushing
passing prey animals. 11 It is likely that Paleoindians made use
of the area as well. 12 Indeed, providing the Coastal Migration
Theory holds true, the corridor leading through the Alcatraz
Triangle connecting the coastal plain with the interior could
have provided the first settlers with an advantageous route for
colonizing California’s Central Valley (Surovell 2003:589). It
would have also allowed easy access to the coastal plain by
interior Paleoindian populations (e.g., Clovis) moving west
from the Central Valley.
Mammoth Rocks also appears to have been located along a
major migration corridor. It is likely that the rubbing rocks sat
29
beside a major game trail linking the interior Santa Rosa Plain
with the coastal plain by way of a pass leading up from the
Russian River and passing between Red and Peaked Hills. The
pass is still used today by State Highway 1. After coming up
from the Russian River by way of the pass, late Pleistocene
animal herds would have looked out across an approximately
20-km wide coastal prairie (at ca. 19,000-15,000 CALYBP), with
the large exposed seastacks of Mammoth Rocks sitting directly
in front of them. The coastal plain would have been marked by
freshwater ponds and estuaries, meandering tree-lined
drainages, localized sand dunes, and other exposed seastacks.
The seastacks offered protection to herd animals, especially on
windy landscapes like the Sonoma Coast.
The Jasper Rock site, like Mammoth Rocks, is situated at
the interior edge of the late Pleistocene coastal prairie. Their
location at the back of the prairie, and along the ecotone
separating the prairie and coastal range, almost guarantees that
both rubbing rock sites were on a major trail corridor that led
north and south along the interior edge of the coastal plain.
The use of this north-south corridor by the megafauna would
have allowed for easier movement and quicker access to
choice locations on the prairie. The Duncans Landing
Rockshelter (CA-SON-348/H) sat near this same hypothetical
north-south trail during the late Pleistocene.
For the past two years, I have been surveying the eroding
bluff of the coastal terrace between Mammoth Rocks and the
Duncans Landing Rockshelter. This has allowed me to
regularly inspect the subsurface stratigraphy of a 5-km transect
traversing the same area that I propose to have once been
characterized by a major north-south game trail. Not surprising,
I have found a number of archaeological sites along this
transect.
One of the often voiced concerns with the Coastal
Migration Theory, and with the Paleoindian occupation of the
late Pleistocene coastline, is that the archaeological sites
associated with such use were inundated by the rising ocean at
the close of the last Ice Age, and thus little can be found of
them. I believe that is only partly true. If Paleoindians
populated the Sonoma Coast, it seems likely that they would
have made great use of the interior edge of the coastal plain.
The area between Mammoth Rocks and the Duncans Landing
Rockshelter was obviously the scene of concentrated
megafaunal activity. As such, the area offered a variety of
resources to the early settlers. For one thing, the area would
have presented rich hunting possibilities. The prospects of
scavenging other predators’ kills may have been an equally or
more important reason for visiting the area. Given the
concentration of animals, the area offered such seldomconsidered
resources as bison dung which may have been used
to fuel campfires and cooking hearths. The area’s proximity to
forested hillsides made it an attractive area to forage for forestedge
resources as well. 13
To date, I have located at least three archaeological sites
along the survey transect where artifacts eroding from the
coastal bluffs (from the subsoil at depths of 50-150 cm) appear
to suggest a considerable antiquity (> middle Holocene?).
Included among the artifacts are a few blade-like flakes with
SCA Newsletter 38(4)