The Todilto Formation is a very distinct unit comprised of a lower limestone unit and a slightly less extensive upper gypsum unit. It was originally defined from Todilto Park, east of the town of Navajo, New Mexico where only the limestone unit is present (Gregory, 1917). The Todilto is mostly confined to NM, but does barely stretch to neighboring states. Lucas, et. al., 1995, formally named the limestone unit the Luciano Mesa Member giving the type locality about half way between Santa Rosa and Tucumcari, NM. Lucas, et. al., 1995 also formally named the gypsum unit the Tonque Arroyo Member, located on the San Felipe reservation (permission needed to visit), about 3.5 miles SE of the Black Mesa Casino near a small gypsum quarry. Lucas, et. al., 2003, pinpointed a specific location within Todilto Park (from Gregory's general description) and defined a the Todilto Fm lectostratotype.

The image above is from just north of San Ysidro, NM. Click HERE for a larger version of the image

The image above is adapted from Lucas et. al., 2003

Gregory, Herbert E., 1917, Geology of the Navajo Country; a Reconnaissance of Arizona, New Mexico, and Utah, USGS Professional Paper 93, 161 pp.

Lucas, Spencer G., Orin J. Anderson, and Clarence Pigman, 1995, Jurassic Stratigraphy in the Hagan Basin, North-Central New Mexico, in New Mexico Geological Society Guidebook, 46th Field Conference, Geology of the Santa Fe Region, p. 247-255.

Lucas, Spencer G., Andrew B. Heckert, and William R. Berglof, 2003, Lectostratotype Section of the jurassic Todilto Formation, Western New Mexico, in Geology of the Zuni Plateau, 54th Field Conference, p. 15-16.