Among the Southern costanoan peoples creation myths resembling those of the Yokuts are found.
"The Religion of the Indians of California"
A. L. Kroeber
They probably had just left costanoan territory, although, to be sure, the exact tribal boundaries are unknown.
"The Aboriginal Population of Alameda and Contra Costa Counties, California"
S. F. Cook
For the remainder of the Northern costanoan territory, since Anza found no inhabitants south of the Livermore Valley, we have to use the figures derived from Crespi: approximately 500 for the interior valleys.
"The Aboriginal Population of Alameda and Contra Costa Counties, California"
S. F. Cook