USGS Open-File Report 2007-1193: 2007 Rocky Mountain Section Friends of the Pleistocene Field Trip—Quaternary Geology of the San Luis Basin of Colorado and New Mexico, September 7

Prologue

Welcome to the 2007 Rocky Mountain Cell Friends of the Pleistocene Field Trip, which will concentrate on the Quaternary geology of the San Luis Basin of Colorado and New Mexico. To our best knowledge, Friends of the Pleistocene (FOP) has never run a trip through the San Luis Basin, although former trips in the region reviewed the "Northern Rio Grande rift" in 1987 and the "Landscape History and Processes on the Pajarito Plateau" in 1996. After nearly a decade, the FOP has returned to the Rio Grande rift, but to an area that has rarely hosted a trip with a Quaternary focus. The objective of FOP trips is to review—in the field—new and exciting research on Quaternary geoscience, typically research being conducted by graduate students. In our case, the research is more topically oriented around three areas of the San Luis Basin, and it is being conducted by a wide range of Federal, State, academic, and consulting geologists.

This year’s trip is ambitious—we will spend our first day mainly on the Holocene record around Great Sand Dunes National Park and Preserve, the second day on the Quaternary stratigraphy around the San Luis Hills, including evidence for Lake Alamosa and the 1.0 Ma Mesita volcano, and wrap up the trip’s third day in the Costilla Plain and Sunshine Valley reviewing alluvial stratigraphy, the history of the Rio Grande, and evidence for young movement on the Sangre de Cristo fault zone.

In the tradition of FOP trips, we will be camping along the field trip route for this meeting. On the night before our trip, we will be at the Great Sand Dunes National Park and Preserve’s Pinyon Flats Campground, a group facility located about 2 miles north of the Visitors Center. After the first day’s trip, we will dine and camp in the Bachus pit, about 3 miles southwest of Alamosa. For the final night (after day 2), we will bed down at La Junta Campground at the Bureau of Land Management (BLM) Wild and Scenic Rivers State Recreation Area, west of Questa, New Mexico, overlooking a majestic canyons of the Rio Grande and Red River.

This is the 48th meeting of the Rocky Mountain Section of FOP, which was initiated by Gerry Richmond (USGS-Denver, deceased) in 1952 (see the following table, which lists all the Rocky Mountain Section field trips). The Rocky Mountain Section has been inactive for three years owing to a series of problems, including an unfortunate cancellation of Dennis Dahms’ trip to the southern Wind River Range in 2005. Hopefully, this year’s trip will provide the logistical initiative and scientific momentum for future Friends of the Pleistocene trips in the Rocky Mountain region.

2007 Rocky Mountain Section Friends of the Pleistocene Field Trip—Quaternary Geology of the San Luis Basin of Colorado and New Mexico, September 7–9, 2007

By Michael N. Machette, Mary-Margaret Coates, and Margo L. Johnson