First-day road log, from Lordsburg to Ruth Mine (Lordsburg district) to Twelve Mile Hill to Rock House Canyon (Pyramid Mountains) to Burgett’s Greenhouses (Animas Valley) to Steins (Peloncillo Mountains)

The first day of the field conference in the Pyramid Mountains examines the difference in magmatic style between the Laramide and mid-Tertiary igneous rocks in southwestern New Mexico. Composite andesite volcanoes with associated intermediate silicic plutons, dikes, and sills dominate the Laramide systems. Large calderas, which erupted rhyolite ignimbrites (ash-flow tuffs) and lavas that are locally interbedded with andesite flows, characterize the mid-Tertiary systems. Stop 1 will be at the Ruth mine, a Laramide polymetallic vein deposit in the Lordsburg district where we will examine the style of mineralization and alteration, and also examine the intrusive relationships of a dacite dike in andesite. We will proceed along the Animas Road to Twelve Mile Hill at Stop 2 where we will have an overview of mid-Tertiary volcanism and caldera activity in Hidalgo County and examine a sequence of ash-flow tuffs erupted from three different calderas. Lunch at Stop 3 will be in Rock House Canyon, where we will have the unique opportunity to enjoy one of the hidden canyons of the Pyramid Mountains and examine more ash-flow tuffs near the northern margin of the Muir caldera. After lunch, we will travel to the Burgett Floral Greenhouses for Stop 4 and observe geothermal resources in action. The tour route between stops 4 and 5 crosses the lower fan delta of ancestral Animas Creek and the floor of pluvial Lake Animas, with its shorelines and Holocene playa-lake features. The first day will end at Stop 5 at the historic town of Steins (pronounced Steens), on the edge of the Steins caldera, for a barbecue dinner.