This study focuses on the interpretation of seismic reflection lines, gravity, and well data in the EstanciaBasin, which is located along the eastern margin of the Rio Grande rift in central New Mexico. Major new data introduced are seven seismic reflection lines provided by the Mobil Exploration and Production Company. The basin began to form during Late Mississippian and Early Pennsylvanian uplift of the Ancestral Rocky Mountains. Laramide-age thrusting and folding occurred west of the basin and may have caused strike-slip movements in the basin. Limited packages of Tertiary rocks occur in local outcrops, and small normal faults associated with the Rio Grande rift are the latest structural features in the basin. An integrated interpretation of the seismic reflection data and other geophysical and geological data make the following observations and interpretations possible: (1) the Pennsylvanian basin is a narrow, fault-bounded trough with a north-south trend;(2) the eastern boundary of this trough is a strike-slip fault that was probably active during formation of the basin; (3) this strike-slip fault was also probably active in the Laramide and possibly active in the Precambrian; (4) there are many prominent dipping reflectors in the Precambrian basement that may represent ductile shear zones, and (5) the effects of the Rio Grande rifting in the area were minor.