Informally named. Name derived from apparent form of huge Thunderbird hanging on southwest side of South Franklin Mountain due to gray limestone of El Paso Group outlining reddish-brown Precambrian rhyolite. Unit occurs on southwest flanks of North and South Franklin Mountains in southern part of Franklin Mountains, El Paso Co, TX, Southwestern Basin-and-Range region. Forms small steep mountain of rhyolite surrounded by and overlapped by Lower Ordovician rocks; 800 m long by 400 m wide. Described as a rhyolite porphyry with basal units including lenses of conglomerate-agglomerate with angular clasts of underlying Llanoria Quartzite. Unconformably underlies Bliss Sandstone. Age is late Precambrian based on Sr-Rb date of 953 +/-13 m.y. by other workers.

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

Rank raised [and formalized] and divided into three newly named formations which are, in ascending order: Coronado Hills Conglomerate, Smugglers Pass and Tom Mays Park Formations. Type locality designated at about 3000 ft northeast of Smugglers Pass in Fusselman Canyon at lat 31 deg 53' 06" and long 106 deg 29' 34". Outcrops from Tom Mays Memorial Park south to McKelligon Canyon area in southern part of Franklin Mountains, El Paso Co, TX, Southwestern Basin-and-Range region. Unconformably overlies Lanoria Quartzite; is youngest late Precambrian unit in area [overlying Phanerozoic units not discussed]. In part correlative with volcanics at Pump Station Hills, Hudspeth Co, TX, about 70 mi east of El Paso. Intrusion by Red Bluff Granite metamorphosed unit to albite-epidote hornfels facies along contact. Geologic map. Stratigraphic column. Geochemistry.

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