As part of a multidisciplinary regional aquifer-system
analysis, a three-dimensional steady-state ground-water-flow
model was constructed for the San Juan Basin in parts of New
Mexico, Colorado, Arizona, and Utah. The model simulated ground-
water flow in 12 hydrostratigraphic units representing all of the
major sources of ground water from aquifers of Jurassic and
younger age.
Ten map reports in the U.S. Geological Survey Hydrologic
Investigations Atlas 720 series were prepared in conjunction with
this investigation. The units that were described in the atlases
were the San Jose, Nacimiento, and Animas Formations; Ojo Alamo
Sandstone; Kirtland Shale and Fruitland Formation; Pictured
Cliffs Sandstone; Cliff House Sandstone; Menefee Formation; Point
Lookout Sandstone; Gallup Sandstone; Dakota Sandstone; and
Morrison Formation. Additional descriptions of the alluvial and
landslide deposits, Chuska and Crevasse Canyon Sandstones, Lewis
and Mancos Shales, Wanakah Formation, and Entrada Sandstone are
included in this report. Much of the information in the HA-720
series was generated from digital computer data bases that were
directly usable by the computer for compilation of input data for
the model. In essence, the major components of the ground-water-
flow model were described and documented in the series of
hydrologic atlases.
The primary finding resulting from the ground-water-flow
simulation was that boundary conditions and internal geometry of
the aquifers are the major controls of steady-state ground-water
flow and hydraulic heads in the San Juan Basin. Another
significant finding was that the computed steady-state ground-
water flux is a very minor component (about 1 percent) of the
total water budget of the basin.
