Abstract: Surface Geology of the Rio Grande Delta, United States-Mexico, a GIS Layer

WERMUND, E. G., and T. A. TREMBLAY
The University of Texas at Austin, Bureau of Economic Geology, Austin, TX

A digital map of surficial depositional systems of the Rio Grande Delta was constructed at a 1:125,000 scale for use in GIS analysis. The seamless spatial layers on the map include political boundaries, transportation, surface hydrology, and geology. The mapped area comprises the area bounded by the confluence of the Rio San Juan and the Rio Grande on the west, Mullet Island, Willacy County, on the north, and Mezquital, Tamaulipas, on the south.

Available digital maps were utilized for the United States part of the study area. Political boundaries and transportation were acquired from the Texas Department of Transportation. The U.S. Geological Survey supplied surface hydrology. For Mexico, we digitized the same data layers from 1:50,000 scale maps published by the Instituto Nacional de Estadistica Geografia e Informatica.

Surficial depositional systems maps were available for four areas, mapped by four different geologists. For the United States 1:125,000-scale maps were compiled from 1:24,000 scale 1950's aerial mosaics; for Mexico 1:125,000 scale maps were compiled from from 1973 and 1994 1:40,000 aerial photographs. In all, four different maps of the depositional systems of the delta were digitized and compiled at 1:125,000 scale.

Problems of map construction and interpretation included (1) making seamless spatial layers using different map presentations at various scales in the United States and Mexico, (2) accounting for effects of Hurricane Beulah (1967) and recent droughts in Mexico, and (3) mapping comparable map units for areas in where rangeland rapidly became cropped agriculture.

AAPG Search and Discovery Article #90932©1998 GCAGS/GCS-SEPM Meeting, Corpus Christi, Texas