Geologic Map of the Bland 7.5-Minute Quadrangle, Los Alamos and Sandoval Counties, New Mexico

Fraser, Goff; Reneau, Steven; Lynch, Scott; Goff, Cathy; Gardner, Jamie; Drakos, Paul; Katzman, Danny

The Bland 7.5 minute quadrangle is located in Los Alamos and Sandoval Counties and straddles the southeastern rim of the Valles caldera in the Jemez Mountains, New Mexico (Fig. 1). Topographically, the quadrangle is bounded by Valle Grande on the northwest, the Sierra de los Valles on the northeast, the Pajarito Plateau to the east and south, the St. Peter’s dome area in the southeast corner, and Bearhead Ridge on the southwest. Geologically, the quadrangle consists of three domains: the southeast moat of Valles caldera represented by Valle Grande, precaldera volcanic rocks of the Jemez volcanic field represented by the mountains in the northeast and southwest, and an extensive plateau of Bandelier Tuff and scattered older volcanic rocks in the center and southeast. Each domain has unique geology as described below. The relatively new Valles Caldera National Preserve (VCNP) occupies the northeastern portion of the quadrangle. Before 2000, the Preserve belonged to the Baca Land and Cattle Company of Abilene, Texas. Access to the Preserve is presently restricted. The rest of the quadrangle is primarily part of the Santa Fe National Forest and the Bandelier National Monument (BNM). Small but significant private lands occur in the area between Pines Canyon and Medio Dia Canyon in the northwest central part of the quadrangle. New Mexico Highway 4 crosses the north part of the quadrangle. Most other areas can be visited by dirt roads. The southwest corner of the quadrangle near the abandoned town of Bland is rather remote and is only accessed by trails. The quadrangle was once home to pre-Columbian Indian cultures (Paleo-Indian, Archaic, and ancestral Puebloan), Spanish land grants, homesteads and scattered ranches. BNM in the eastern part of the quadrangle contains numerous archeological sites that were protected in 1916 to preserve prehistoric, scientific and scenic values. VCNP occupies the northwest part of the quadrangle (Martin, 2003) and was created by the Valles Caldera Preservation Act of 2000 to preserve and protect the historic Baca Ranch and the geologically famous Valles caldera of the Jemez Mountains volcanic field. The VCNP is managed for limited public recreation, and for elk hunting, cattle grazing, fishing, and scientific study. Gold and silver were successfully extracted from the Cochiti Mining District near Bland in the late 1800s to early 1900s (Hoard, 1996) and precious metal exploration has been conducted sporadically on National Forest lands to the present. Geothermal energy was explored but not developed on both VCNP and National Forest lands in the 1960s to 1980s (Laughlin, 1981; Goff and Gardner, 1988). Presently, timber is harvested and pumice is mined on National Forest lands. The objectives of the present study are to provide detailed geologic mapping for the VCNP and the BNM, and to contribute quadrangle maps for the New Mexico State Map Program. The geology of the southeast part of the quadrangle was mapped previously (Goff et al., 1990) but was field checked and updated for the present project. The rest of the quadrangle was mapped during parts of 2003, 2004 and 2005. Regional geology and stratigraphy have been previously published by Griggs (1964), Bailey et al. (1969), Smith et al. (1970), Kelley (1978), Gardner (1985), Gardner and Goff (1984) and Gardner et al. (1986). Adjacent and nearby NM State Map quadrangles have been published by Goff et al. (2002, 2005), Kempter and Kelley (2002), Osburn et al. (2002), Kelley et al. (2003) and Lynch et al. (2004). Broxton and Vaniman (2005) presented a geologic framework for aquifers beneath the southern Pajarito Plateau.

Geologic Map of the Bland 7.5-Minute Quadrangle, Los Alamos and Sandoval Counties, New Mexico

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