Named as the basal member of the newly named Superstition Tuff for exposures in Siphon Draw, the type section, secs 7 and 8, T1N, R9E, Pinal Co, AZ in the Basin-and-Range province. Type lies within the resurgent dome of the Superstition cauldron. Conformably onlaps a series of unnamed dacite domes, lavas, and autoclastic breccias [age not stated]. Younger rocks not preserved at type. Is unconformably overlain by nonwelded rhyolite ash flows and epiclastic breccias of the newly named Geronimo Head Formation in the Superstition Wilderness area. The next younger member of Superstition is the Dogie Spring member (new). Is approximately 670 m thick. Consists of quartz latite ash-flow tuff. Nine distinct partings at type are separated by thin dacite breccias or air-fall lenses. Distinguishable from other members of Superstition by its mode of quartz >, plagioclase > sanidine with accessory sphene, zircon, apatite, and magnetite. F-T dates on zircon from top and bottom of member are 24.5 +/-0.5 m.y. and 24.2 +/-0.9 m.y., respectively. K-Ar date on biotite of 22.6 +/-1.0 m.y. obtained from Black Mesa area. Geologic map; columnar section. Miocene age.

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

Siphon Draw Member of the Superstition Tuff of Stuckless and Sheridan (1971) is adopted. Age is Miocene.

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