TERTIARY IGNEOUS ROCKS
The trans-Pecos mountain area was the scene of much igneous activity during early Tertiary time. Great sheets of lava were spread over the Davis Mountains and adjacent areas, across a surface of Cretaceous and older rocks (for location of Davis Mountains, see fig. 1). Both the lavas and sedimentary rocks are penetrated by a host of small to large intrusive masses, some of which are far removed from the Davis Mountains volcanic field. In the Guadalupe Mountains region, however, little record remains of these events, and very little igneous activity took place there. One small intrusive plug was found within the area studied, and only a few have been found elsewhere in the mountains.
This plug, discovered by H. C. Fountain, is situated in the Delaware Mountains, in a small ravine half a mile north of Lamar Canyon and 1-1/2 miles east of the junction of Cherry and Lamar Canyons (pl. 3). It forms a low ridge several hundred feet long, and cuts sandstones not far above the level of the Rader limestone member of the Bell Canyon formation. The sandstones have been tilted, baked, and silicified for about 10 feet from the edge of the plug. The rock itself is light gray and aphanitic and is probably a trachyte.
There is possibly another, still buried intrusive in the Guadalupe Mountains beneath the northeast slope of Lost Peak (pl. 3). Here, at the prospect known as the Calumet and Texas Mine, the Carlsbad limestone has been replaced by copper, lead, zinc, and iron minerals, which probably emanated from an igneous source beneath.
Northeast of the area studied, in the northeast part of T. 26 S., R. 24 E., Eddy County, New Mexico, a dike of igneous rock cuts the anhydrites of the Castile formation. I have not visited this locality, and know nothing of the character of the rock.
Last Updated: 28-Dec-2007