BIG BEND RANCH STATE PARK AS A CLASSROOM FOR AN INTRODUCTORY PETROLOGY COURSE

The Big Bend Ranch State Park (BBRSP) offers an excellent location for geologic field trips for many different academic and professional levels of interest. The geology of the park includes excellent exposures of rocks of Paleozoic, Mesozoic, and Cenozoic age. Over the past decade, our sophomore level lithology (petrology) class has used the park as a field trip destination for the purpose of introducing students to field geology and techniques. The trip is usually offered in late October or early November, and lasts from Thursday to Sunday afternoons. The trip begins with a short lecture at Las Cuevas Amarillas, where we discuss aspects of the Leyva Canyon volcano. Students are required to complete a short assignment, including the construction of a stratigraphic column of an ash-flow tuff and lahar sequence. We then proceed to our camp site near the Sauceda ranch headquarters. On Friday, we travel into Fresno canyon to the Arroyo Segundo for our first major exercise. Here, the students are required to complete a geologic map of a sequence of tuffaceous sediments, conglomerateS, and trachyte lava flows. We hike directly west into the canyon, and since the rock units have a 3-4 degree west dip, we are able to walk across each of the contacts. The students are instructed on how to draw the proper “v” shaped contacts on their topographic base map. On Saturday, we drive into the Solitario, a 35-36 Ma laccolith/dome/caldera. Assignments include a stop to view a rhyolite sill emplaced along the Paleozoic – Mesozoic contact in the Left-hand shutup a hike into the lower Shutup. At this stop, we hike through caldera collapse material, Paleozoic sediments, and into the lower part of the Cretaceous. On Sunday, we visit the Bofecillos mountains, discuss the volcanic evolution of the area and return to Alpine. Though often overlooked as a field trip destination due to the popularity of the nearby Big Bend National Park and to the remote nature of the stops described here, the BBRSP provides an ideal setting for geologic field trips.