Third-day road log: From Santa Fe to the Cerrillos Hills, Cerrillos and the Ortiz Mountains
— Paul W. Bauer, Stephen R. Maynard, Gary A. Smith, David L. Giles, Spencer G. Lucas, James M. Barker, Edward W. Smith, and Frank E. Kottlowski

The Day 3 trip takes us southeast from Santa Fe, through the Cerrillos Hills and into the Ortiz Mountains. For the first 6 mi we travel on 1-25 over the Pliocene-early Pleistocene Ancha Formation of the uppermost Santa Fe Group. At La Cienega exit we turn southeastward into the Cerrillos Hills, which are composed of prerift subvolcanic intrusions of monzonite and related rocks dated at 34-30 Ma that represent the northern end of the San PedroOrtiz porphyry belt. The Cerrillos Hills intrusions have domed the pre-middle Oligocene strata, so that average dips on the southeast flank are to the southeast. Farther east along Galisteo Creek toward Galisteo, dips are to the west (as they are in the Tesuque Fm north of 1-25 from Santa Fe to west of the 1- 25- Cerrillos Road junction). This faulted asymmetrical syncline (the Santa Fe embayment, the southeasternmost part of the Espanola Basin) is truncated to the southeast by the Tijeras-Caiioncito fault system. Although zinc, lead, silver, copper and gold have been mined from the Cerrillos Hills, the district is most prominent for its fine turquoise. At Stop 1 we will visit the Tiffany Mine at Turquoise Hill, from which more than $2,000,000 worth of high-grade gem turquoise was removed in the 1890s.

From the Tiffany Mine, we travel eastward across the Ancha Formation and surface sands and gravels to NM-14 south. Deeply incised arroyos to the west expose the basal Tertiary unit in the area, the Eocene Galisteo Formation of sandstone, mudrock and fresh-water limestone. The Galisteo is conformably overlain by intermediate-volcanic agglomerates, breccias and fanglomerates of the Oligocene Espinaso Formation. The Espinaso is syndepositional with igneous activity of the San Pedro-Ortiz porphyry belt, extending from La Cienega southward to South Mountain, east of the Sandia Mountains. At Stop 2 we visit the studio of famed sculptor Allan Houser, who turned New Mexico alabaster and Italian marble into stunning sculptures.

We continue south through the steeply dipping Galisteo Formation to Stop 3, just east of Cerrillos, where we will discuss the relationship between mid-Tertiary igneous activity, deformation, and sedimentation. The trip continues south from Cerrillos onto a gravel road leading to the gold mines of the Ortiz Mountains. As we climb out of the valley of Galisteo Creek, we pass from the Galisteo Formation to the unconformably overlyingTertiary-Quaternary Tuerto Gravel, a coarse cobble conglomerate that was derived from the Ortiz and San Pedro Mountains. Stop 4 finds us at the inactive Cunningham Hill open pit gold mine in the northeastern Ortiz Mountains. Gold Fields Mining Corporation operated the mine from 1979 to I 987, producing approximately 250,000 oz of gold. Brecciated quartzite derived from the Galisteo Formation adjacent to the volcanic vent of Dolores Gulch is the host rock. We will examine the ore deposit and discuss mine-related environmental concerns and the status of remediation efforts.

From Cunningham Hill the tour continues southwestward through the intruded Cretaceous sedimentary section of the Ortiz Mountains to Stop 5 at Carache Canyon, where LAC Minerals has identified a mineral resource of one million ounces of gold, mainly in fractured and mineralized sills related to a spectacular collapse breccia.