/Arroyo Seco Formation of Barren Mountains Group. Poorly consolidated fanglomerate containing cross-bedded sand lenses with gravel- to boulder-size volcanic rock clasts in sandy matrix. Locally contains over 50 percent metamorphic-igneous complex rocks which give unit light gray color. Is lower formation of Barren Mountains Group. Underlies Vinagre Formation (new), upper formation of Barren Mountains Group. Unconformably overlies Tolbard Fanglomerate. Age is Pliocene(?) to Pleistocene(?) [no basis given].
[Type locality not designated. Origin of name not stated, but probably named from Arroyo Seco, north of study area.] Study area in Midway Mountains [local name for unnamed mountains west of Midway Well, northwest of Vinagre Wash, and south of Milpitas Wash, in T. 11 S., R. 20 E., Quartz Peak 7.5-min quadrangle], Imperial Co., southern CA. Name credited to M.C. Garner and others' 1960 report submitted to Southern Pacific Land Company.
[Name preempted by Arroyo Seco Gravel of Piper and others (1939) in northern CA.]

Source: Modified from GNU records (USGS DDS-6; Menlo GNULEX).