Tertiary and Quaternary stratigraphy of the northeast plateau, Espanola Basin, New Mexico
— Kim Manley

The Espanola basin is the northernmost Rio Grande rift basin in New Mexico (Manley, 1979). It is both a structural and a topographic basin, in which erosion has exposed a thick sequence of predominantly Miocene to Pleistocene sedimentary rocks.

 

This paper discusses the Tertiary and Quaternary stratigraphy of the northeast part of the Espanola basin. Precambrian, Pennsylvanian, Tertiary and Quaternary rocks are exposed in the area. As a result of my recent mapping, the sedimentary rocks previously mapped (Miller and others, 1963) as the Pleistocene Ancha Formation and part of the underlying Miocene Tesuque Formation have been reassigned to (fig. 1):

 

1) The Cejita Member of the Tesuque Formation

2) A piedmont facies of the Tesuque Formation

3) High surface gravel deposits of Pliocene to early Pleistocene age

4) Quaternary gravel deposits (including the Santa Barbara, Santa Cruz and Chamisal gravel deposits)

 

Each of these units is discussed in the following text. The use of the term Ancha Formation for the varied gravel deposits is considered inappropriate and is not used in this report.

 

The northeast part of the Espanola basin (fig. 2) is a fan- shaped plateau with an apex near Jicarilla Peak; it extends from the Sangre de Cristo Mountains on the east to the Rio Grande on the west. The plateau is bounded on the south by
the Rio Quemado and the Santa Cruz valley; on the northeast by the Picuris Range; and on the north by an erosional basin, the Dixon sub-basin.

 

The northeast plateau has received little study. Galusha and Blick (1971) referred to the area as the Picuris re-entrant fan, but did not map it. They assigned sedimentary rocks in the western Dixon sub-basin to the Ojo Caliente Sandstone Member of the Tesuque Formation and to gravels overlying the Truchas pediment (Galusha and Blick, 1971, p. 67, 70 and 96). Miller and others (1963) mapped the sedimentary rocks in this area and assigned them to three formations: the Tertiary Picuris and Tesuque formations and the Pleistocene Ancha Formation. The Ancha Formation was described as "remnants of a once-continuous sheet of unconsolidated gravel" that is locally more than 90 m thick (Miller and others, 1963, p. 51).