Named for Flag Spring [not shown on geologic map] in Cottonwood Canyon, T19N, R20W, Mohave Co, AZ, Plateau sedimentary province. No type locality designated. Overlies Gold Road latite (new). Underlies Meadow Creek trachyte (new). Forms a reddish-brown cliff. Not represented south of Sitgreaves Pass in sec 12, T19N, R20W. Has a maximum thickness of about 250 ft. Not extensive. Geologic map. [No other descriptive information included. Author expected to give a more complete account in a future report, but the "future" report was never published.] Tertiary age.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Flag Spring Trachyte redescribed as Flag Spring Quartz Latite. Consists of iron-rich, alkalic to subalkalic quartz latite flows, agglomerates and flow breccias. Resembles Esperanza Quartz Latite. Contains 10 to 25 percent phenocrysts of plagioclase, biotite and minor hornblende. Has high strontium content. Mapped (geologic maps) with the overlying Meadow Creek Quartz Latite (redescribed), and the Sitgreaves Tuff northeast of Oatman, Mohave Co, AZ in the Plateau sedimentary province. Overlies Cottonwood Formation (redescribed). Chemical analyses. Age modified from Tertiary to Miocene.

Source: GNU records (USGS DDS-6; Denver GNULEX).