U.S.-Mexico Border Geologic Framework

Science Center Objects

The primary objective of the U.S.-Mexico border project is to provide framework geology through geologic mapping activities to support border-wide science investigations including assessing and evaluating groundwater, energy and mineral, and ecological resources, and identifying and investigating natural hazards, including landslide, earthquake, wildfire, and flood hazards.

Active Project Task: Geologic investigations of the Upper Santa Cruz basin, Arizona

The Santa Cruz River is a bi-national watershed located in southern Arizona, U.S.A., and northern Sonora, Mexico. The headwaters of the Santa Cruz are in San Rafael Valley in Arizona, from where the river flows south into Sonora for 35 miles, and then it crosses back into the U.S. east of Nogales Arizona/Sonora. Much of the Santa Cruz River once had natural perennial flow, but with the influx of settlers in the 1800’s, anthropogenic and environmental stressors contributed to decreased flow and degraded the land and river through logging, overgrazing, mining, and ground-water pumping.

Objectives

The main objectives of the Upper Santa Cruz basin task (Fig. 1) are to carry out new geologic mapping and to compile existing geologic mapping and provide the geologic framework in the study area primarily in support of groundwater investigations. Geologic mapping is the fundamental dataset in understanding ground-water flow in the basin and in defining the geometry and thickness of the basin-fill and alluvial aquifers. The sister cities of Nogales Arizona and Nogales Sonora depend on the aquifers for safe drinking water supplies and other domestic, industrial, and agricultural uses. Anthropogenic and environmental stressors threaten the San Cruz aquifer, including effluent in Nogales Wash from the Nogales urban areas, and toxic metals from past mining activities in the Sonoita Creek and Patagonia areas (fig. 2). Rapid population growth and declining recharge to basin aquifers in the Nogales area has increased the demand for additional groundwater resources. this demand is predicted to escalate in the future due to higher seasonal temperatures, longer droughts, and decreased river baseflow. Geologic framework is also extremely important in studying and detecting concealed mineral deposits, and in understanding flood hazards in Nogales Wash and Santa Cruz River. Geologic framework studies contribute significantly in detecting and predicting the location of illegal tunnels beneath the international border. New mapping in the Upper Santa Cruz basin will also form the basis for evaluating landscape and habitat dynamics in this part of the Borderlands.

Our geologic mapping approach depends heavily upon existing geologic maps and reports in the region. New mapping will focus on basin-fill deposits of Quaternary and Tertiary age, which form the Santa Cruz aquifer. Studies will also focus on mapping and evaluating faults and fracture systems to better understand their control of ground-water flow, aquifer recharge and discharge, and contaminant transport.

 

Upper Santa Cruz basin study area

Figure 1: The upper Santa Cruz basin study area in Arizona extends over the Sells, Fort Huachuca, Nogales and Atacosa 1:100,000-scale quadrangles. To gain a better understanding of the basin, we began the project by conducting detailed geologic mapping of the Rio Rico and Nogales (Arizona) 1:24,000-scale quadrangles (outlined in red). Through this mapping, we significantly re-defined the stratigraphy of the Miocene Nogales Formation, and have characterized the formation by analyzing samples for geochronology, porosity, saturated hydraulic conductivity, physical properties, and fabric analyses based on petrographic studies. Results of our mapping the Rio Rico and Nogales quadrangles indicate that parts of the Nogales Formation may provide new, deeper sources of groundwater for the Nogales area. We conducted integrated geophysical studies in the quadrangles by analyzing airborne transient electromagnetic data, high resolution aeromagnetic data, gravity data, and magnetic susceptibility data collected within the study area. These data were critical in defining the subsurface basin geometry, hydrostratigraphic units, and the location of concealed faults which may control groundwater flow. The major product for the overall project will be a regional-scale geologic map of the Arizona part of the upper Santa Cruz basin (shown in white).

Our project collaborates directly with Arizona Department of Water Resources, the City of Nogales Utilities Department, and the USGS Arizona Water Science Center in modelling, model calibration, assessment, and water resource evaluation in the basin. Our project was contacted by Department of Homeland Security (DHS) and U.S. Border Patrol who requested our geologic expertise to help detect and predict the location of illegal tunnels beneath the border, and DHS used our geologic map of the Rio Rico and Nogales quadrangles in building geologic models along the border.

 

Preliminary mapping of the Upper Santa Cruz basin study area

Figure 2: Preliminary compilation of existing geologic mapping in study area: red and pink colors generally represent Cenozoic volcanic and intrusive rocks; green, purple, and blue colors are Mesozoic and Paleozoic sedimentary, volcanic, and intrusive rocks; yellow colors are Quaternary and Tertiary basin-fill deposits; and tan and brown colors are Proterozoic igneous rocks.

 

Photo of Rio Rico, Arizona

Figure 3: Rapid population growth in the Rio Rico and Nogales areas has increased the demand for groundwater resources in the upper Santa Cruz basin. New homes in Rio Rico with San Cayetano Mountains in background. (Credit: William R. Page, Public domain.)

Our project has developed a 3-D geologic model of the Rio Rico and Nogales 7.5' quadrangles to investigate groundwater resources in the upper Santa Cruz basin. Analysis of the model resulted in defining the geometry and thickness of the basin fill and alluvial aquifers, which provide water to Nogales and surrounding communities. We presented a poster at the 2016 Geological Society of America Annual Meeting, describing the  three-dimensional hydrogeologic framework model of the Rio Rico and Nogales 7.5' quadrangles, Upper Santa Cruz Basin, southern Arizona (Page. W.R., Bultman, M., Gray, F., Menges, C., VanSistine, P., and Pantea, M., 2016, Three-dimensional hydrogeologic framework model of the Rio Rico and Nogales 7.5' quadrangles, Upper Santa Cruz Basin, southern Arizona: GSA Abstracts with Programs, v. 48, no. 7).

Animation created in EarthVision 3D Viewer using data from the USGS report Page and others (2018)

Figure 4. The movie previews a 3-D hydrogeologic model of the Rio Rico and Nogales 7.5’quadrangles Arizona, included in USGS Scientific Investigations Report 2018-5062 (Page and others, 2018). The model was built in EarthVision (Dynamic Graphics, Inc.) 3D modeling software. The Rio Rico and Nogales quadrangles model contains 3D Viewer software enabling viewing geologic data interactively in 3D space and the ability to sequentially slice through and rotate the modeled geology to help explain complexities in the basin aquifers and basement.

Completed Project Tasks— Big Bend National Park Geologic Map and U.S.-Mexico Border Environmental Health Initiative (Geology Component)

 

Big Bend National Park Geologic Map

Image of the Geologic Map of Big Bend National Park, Texas

Geologic Map of Big Bend National Park, Texas, winner of 2012 Shoemaker Award for Communication in the Graphic Product catagory.

Big Bend National Park is the 8th largest national park within the contiguous United States and hosts about 350,000 visitors annually. The Park contains a variety of world-class volcanic, structural, geomorphological, and paleontological sites. Mapping by Maxwell and others (Maxwell, R.A., Lonsdale, J.T., Hazzard, R.T., and Wilson, J.A., 1967, Geologic map of the Big Bend National Park, Brewster County, Texas: University of Texas at Austin Bureau of Economic Geology Publication 6711, scale 1:62,500) synthesized earlier work, but updated mapping was required to investigate unresolved issues related to volcanic and surficial statigraphy as well as the volcanic, plutonic, and tectonic evolution of the park.

An updated map of the park provides the National Park Service with a digital geologic map dataset to address resource management issues. These issues include land use planning, surface and ground-water quality and quantity, wildlife and plant inventories and monitoring, habitat sustainability, and ecosystem and antiquities preservation.

Mapping of Big Bend National Park was a cooperative effort between federal, state and academic agencies, including the National Park Service, Texas Bureau of Economic Geology, and numerous universities. The project was funded by the National Park Service and the USGS National Cooperative Geologic Mapping Program.

 

 

 

U.S.-Mexico Border Environmental Health Initiative (Geology Component)

The vast U.S.-Mexico Borderlands are a unique and extremely fragile region extending 1,952 miles from the Pacific Ocean to the Gulf of Mexico. The Borderlands encompass a diverse array of physical settings and habitats that include wetlands, deserts, rangeland, mountains, and forests which are unique in terms of their water, mineral, and biological resources. Rapid population growth and economic development and land-use changes are pushing the limits of environmental sustainability and the quality of human and wildlife health in the Borderlands. To allow for continued growth while protecting natural resources, habitats, and fostering a high quality of life, it is imperative for U.S. and Mexican citizens, governmental agencies, and local decision makers to focus collaboratively on systematic, interdisciplinary scientific studies, such as those carried out for the U.S.-Mexico Border Environmental Health Initiative, to address the critical Borderlands issues. The main product of the U.S.-Mexico Border Environmental Health Initiative is USGS Circular 1380, United States–Mexican Borderlands—Facing tomorrow’s challenges through USGS science. The Circular is the first comprehensive science plan for the borderlands region, highlighting current and past USGS research that has helped advance our understanding of critical border issues.

The Border Environmental Health project acquired, evaluated analyzed, and provided earth, biologic, and human health resources data for the Borderlands within a GIS framework using an Internet map service (IMS) to further our understanding of possible linkages between the physical environment and public health issues. The IMS provides information to researchers, planners, managers, and citizens to make informed decisions concerning human health issues in the Borderlands region, and IMS users may incorporate most available data layers into their own geospatial analyses.

The main Geologic Discipline compiled bi-national geologic maps and integrated data sets of the U.S.-Mexico Borderlands and investigated potential linkages between geology and human and wildlife health. The study area for the work cited in the project publication below was in southern Texas and northern Mexico (fig. 4).

Bi-national geologic map from USGS Open File Report 2009-1015

Figure 4: Bi-national geologic map from USGS Open File Report 2009-1015 (Page and others, 2009) in southern Texas and northern Mexico. To better understand and begin to analyze the relationships between naturally occurring geologic materials, anthropogenic processes, and human and wildlife health, point data layers were added to the map showing the location of active and inactive mines, mineral prospect/occurrences, smelters, coal-burning and gas-fired power plants, and oil and gas wells.