Marathon Aquiferinteractive map

Aquifer Facts

  • Aquifer type: unconfined with locally confined areas
  • Area of aquifer: 391 square miles
  • Proportion of aquifer with groundwater conservation districts: 100 percent
  • Number of counties containing the aquifer: 1


The Marathon Aquifer, a minor aquifer, occurs entirely within northcentral Brewster County. The aquifer consists of tightly folded and faulted rocks of the Gaptank Formation, the Dimple Limestone, the Tesnus Formation, the Caballos Novaculite, the Maravillas Chert, the Fort Pena Formation, and the Marathon Limestone. Although maximum thickness of the aquifer is about 900 feet, well depths are commonly less than 250 feet. Water in the aquifer is under unconfined conditions in fractures, joints, and cavities; however, artesian conditions are common in areas where the aquifer rocks are buried beneath younger formations. The Marathon Limestone is at or near land surface and is the most productive part of the aquifer. Many of the shallow wells in the region actually produce water from alluvial deposits that cover parts of the rock formations.

Total dissolved solids range from 500 to 1,000 milligrams per liter, and the water, although very hard, is generally suitable for most uses.

Groundwater is used primarily for municipal water supply by the city of Marathon and for domestic and livestock purposes.


ID Date Type Description
Texas Aquifers Study 12/31/2016 Legislative Report Texas Aquifers Study: Groundwater Quantity, Quality, Flow, and Contributions to Surface Water
R-356 12/1/2001 TWDB numbered report Aquifers of West Texas
AA06-01 6/10/2008 Aquifer assessment Water-level decline scenarios for the Capitan Reef Complex, Marathon, Rustler, Presidio-Redford Bolson, Edwards-Trinity (Plateau), and Diablo Plateau aquifers in Groundwater Management Area 4
AA09-09 8/31/2010 Aquifer assessment Desired future condition scenarios for the Marathon Aquifer in Groundwater Management Area 4
R-380 7/1/2011 TWDB numbered report Aquifers of Texas
GT13-028_TERS 1/15/2014 GAM task - Total Estimated Recoverable Storage Total Estimated Recoverable Storage for aquifers in Groundwater Management Area 4