New Mexico Geological Society Annual Spring Meeting — Abstracts

Fractures in the southern Sacramento Mountains, south central New Mexico, influence both surface and ground water flow. Fractures are often assumed to control water movement, but the relationships of stream orientation or spring discharge locations with fractures are rarely quantified. This study combines fracture measurements in the field with GIS analysis to assess fracture control on stream orientations and spring discharge locations. One hundred seventy fractures were measured at 70 sites. They primarily consist of opening mode joints with NE-SW and NW-SE orientations. These orientations are consistent with previous regional structural interpretations based on fault kinematics (Howell 2003). East dipping strata, at the surface consisting of San Andres Formation limestone and Yeso Formation limestone and mudstone, cause most streams in the study area to flow generally eastward towards the Pecos River. However, about 1/3 of the stream segments are parallel to one of the two dominant joint sets. The joint-parallel stream segments form prominent peaks on plots of total stream length vs. orientation. In addition, the Sacramento River flows southeast, along the axis of a graben.

Joint-parallel stream segments selected from streams mapped with a DEM are up to 900 meters in length and are parallel to fractures observed in the field. The abundance of surveyed springs throughout the study area decreases logarithmically with distance from joint parallel stream segments. These findings indicate that joints strongly affect surface and groundwater flow, and most likely recharge. Future field observations will quantify the effects of fractures on the interaction between surface and ground water by measuring stream flow rates upstream and downstream of joint-parallel stream segments.