Pyroclastic rocks in Alturas basin, Modoc County, California, are herein named /Warm Springs Tuff Member of Alturas formation. Member is 100 to 400 feet thick sequence of gray to brown, massive pumice lapilli tuff, light-colored sandstone, and resistant rimrock areas. Includes numerous chimney rocks caused by weathering of massive ash-flow tuff. Overlies unnamed lower member; underlies unnamed basalt member, both of Alturas formation. Age is Pliocene and Pleistocene [basis for age assignment not stated.]
[Name preempted by Warm Springs Formation of Lupher (1941) in OR.]
Source: Modified from GNU records (USGS DDS-6; Menlo GNULEX).
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