Pg. A34-A35, A50-A55. Putah Tuff Member of Tehama Formation. Adopted and assigned as member of Tehama Formation in its geographic extension southward into central California. Putah has similar stratigraphic position with Nomlaki Tuff Member of Tehama in northern California but is neither coextensive nor correlative. Consists of well stratified and commonly cross-bedded volcanic tuff; in places contains rounded hard pumice lapilli and detrital sedimentary material derived from underlying part of the Tehama, indicating that the Putah was water laid and reworked. Thickness up to 50 feet (15 m). Age is late Pliocene based on a radiometric (K-Ar) date of 3.3 Ma.
Type locality: roadcut on north side of Putah Creek, along CA Highway 128, in sec. 36, T. 8 N., R. 2 W., Yolo Co., west-central CA. Name credited to W.L. Miller (1966 Univ. California-Davis MS thesis).
See also geologic map by E.J. Helley and D.S. Harwood (USGS Misc. Field Studies Map MF-1790, 1985).

Source: Publication; US geologic names lexicon (USGS Bull. 1520, p. 248).