Colmena Tuff mapped as one of seven formations of Vieja Group in the Sierra Vieja area, Presidio Co, west TX in the Permian basin. Vieja Group is shown on the Correlation of Map Units as consisting of (ascending): Gill Breccia, Colmena Tuff, Buckshot Ignimbrite, Chambers Tuff, Bracks Rhyolite, Capote Mountain Tuff, and Mitchell Mesa Welded Tuff. Colmena is a fine-grained, thin-bedded tuffaceous sandstone and pebble-to-boulder limestone-and-sandstone conglomerate; contains some nonmarine limestone, silty claystone, and glassy flow rock, pale red to white. Is mostly tuffaceous sandstone and limestone in the south, mostly conglomerate in the north. Mapped with Jeff Conglomerate (Jeff not separately mapped). Thickness as much as 450 ft. Contains Eocene vertebrate fossils. [Author states that correlation of volcanic rocks from area to area on Marfa sheet is uncertain--little attempt is made to correlate between areas. The rocks are described by area.] Colmena is of Eocene age. Geologic map.

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

Term "Vieja group" not used in report which lies in Culberson Co, TX in the Permian basin. Revised in Van Horn Mountains and Sierra Vieja areas to exclude an ash-flow tuff, called Buckshot Ignimbrite, as well as several small isolated outcrops of basalt. Includes conglomerate, tuff and tuffaceous sedimentary rocks. Clasts in the conglomerate are as much as 1 m in diameter and are exclusively from Cretaceous rocks. Deposited on an erosional surface of moderate relief developed on top of Cretaceous rocks. Underlies Buckshot Ignimbrite. Of probable Eocene age. Geologic map. Correlation chart.

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