Rocky Mountain Section - 64th Annual Meeting (9–11 May 2012)

Paper No. 18
Presentation Time: 8:00 AM-5:30 PM


ARMOUR, L.K., Geology, The University of Texas at El Paso, 500 W University Ave, El Paso, TX 79902 and LANGFORD, Richard P., The University of Texas at El Paso, 500W University Ave, El Paso, TX 79968,

Along both flanks of the Franklin Mountains, terraces uplifted along boundary faults exhume basin floor sediments, inter-tonguing with alluvial fans. Because the Palo-basin floor must have had a low gradient, estimated at less than 0.001, the terraces provide a record of long-term uplift of the Range. The goal of this research is to measure the long-term deformation of these Pliocene and Early Pleistocene terraces. Most extensional ranges are flanked with alluvial fans and bajadas that create an irregular mountain front. In the southern Rio Grande Rift, the sediment from the river buried the alluvial fans and juxtaposed horizontal playas and low-gradient floodplains with the bedrock of the mountains. This presents an opportunity to document long-term deformation of these low-relief surfaces.

There are three areas that warrant examination for this research. We initially began with the western slope of the Franklin Mountains and compared slope and elevation to the plain on the western side of the Río Grande. The next two steps will be to compare the terraces along the east side of the Franklin Mountains to terraces on the west side of the mountains; third, we will examine the younger terraces of the Robledo Mountains in southern New Mexico and compare them to our original findings along the western slope of the Franklin Mountains. These show higher uplift in the center of the range, with the terraces generally mimicking range topography. They also exhibit, a previously documented 2-degree tilt to the west, reflecting the more active uplift on the eastern boundary fault.