U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY Miscellaneous Field Studies Map MF–2405 Version 1.1 GEOLOGIC MAP OF THE SANTA ANA PUEBLO QUADRANGLE, SANDOVAL COUNTY, NEW MEXICO By Stephen F. Personius 2002 The Bernalillo NW quadrangle is located in the northern part of the Albuquerque basin, which is the largest basin or graben within the Rio Grande rift. The quadrangle is underlain by poorly consolidated sedimentary rocks of the Santa Fe Group. These rocks are best exposed in the southwestern part of the quadrangle in the Rincones de Zia, a badland topography cut by northward-flowing tributary arroyos of the Jemez River. The Jemez River flows through the northern half of the quadrangle; extensive fluvial and eolian deposits cover bedrock units along the river. The structural fabric of the quadrangle is dominated by dozens of generally north striking, east and west-dipping normal faults and minor folds associated with the Neogene Rio Grande rift. The geology of the Bernalillo NW quadrangle was mapped as part of the USGS Middle Rio Grande Basin project to explore the geologic framework of water resources in the region. This publication consists of a map sheet and a geospatial database. The map sheet includes the principal map, one cross section, a diagram showing stratigraphic correlation of map units, a description of map units, discussion, list of references, an index map that shows the location of the study area within the State of New Mexico, and one small table. The description of map units, discussion, table, and list of references are included with this text-only file. DISCUSSION The Santa Ana Pueblo quadrangle is located in the northern part of the Albuquerque basin, which is the largest basin or graben within the Rio Grande rift in New Mexico. The quadrangle is underlain by poorly consolidated sedimentary rocks of the Santa Fe Group and is dominated by Santa Ana Mesa, a volcanic tableland underlain by basalt flows of the San Felipe volcanic field. The San Felipe volcanic field is the largest area of basaltic lavas exposed in the Albuquerque basin (Kelley and Kudo, 1978). STRUCTURE The structural fabric of the quadrangle is dominated by dozens of generally north striking, east- and west-dipping normal faults associated with the Neogene Rio Grande rift. Many of these faults form resistant fault scarps where they offset basalt flows underlying Santa Ana Mesa, but most faults in the underlying Santa Fe Group sedimentary rocks are poorly expressed. Exceptions are the Santa Ana fault and an unnamed fault in the northwestern part of the quadrangle, where prominent ridges mark the surface expression of the fault due to enhanced silica and (or) calcium carbonate cementation in the footwall. Another major fault is the down-to-the-east Tamaya fault, herein informally named after the local term for the nearby old Santa Ana Pueblo. This fault was not previously identified, but rather was mapped as a contact between contrasting subunits of Santa Fe Group rocks (Soister, 1952; Spiegel, 1961; Smith and others, 1970; Kelley, 1977). The Tamaya and Santa Ana faults are related en echelon structures; the Santa Ana fault dies out in the adjacent Bernalillo NW quadrangle (Koning and Personius, 2002), just south of a complex fault stepover with the Tamaya fault. The Tamaya fault can be traced in numerous exposures southward to the Jemez River and is mapped continuously beyond the southern quadrangle boundary on the basis of a prominent anomaly in high-resolution aeromagnetic data (U.S. Geological Survey and SIAL Geosciences, Inc., 1997). The Tamaya fault is exposed in a roadcut along U.S. Highway 550, where it has been erroneously mapped as the Luce fault (Kelley, 1977; Pazzaglia and others, 1999; Connell and others, 2000). The Tamaya fault has the most offset of any fault in the quadrangle, although absence of correlative units exposed across the structure prevent measurement of total throw. The fault may also cut Quaternary 1 deposits, because it coincides with a 5-m-high, east-facing scarp in old arroyo alluvium (unit Qalo) about 500 m north of the Jemez River. The age of this alluvium is unknown, but probably is middle Pleistocene or younger, because the deposit underlies a fan that covers old deposits of the Jemez River (unit Qaj1) that probably are younger than deposits containing the ≈640-ka (Lanphere and others, 2002) Lava Creek B ash in the headwaters of the Jemez River (Rogers, 1996; Rogers and Smartt, 1996). Other prominent structures in the quadrangle are the Luce and Algodones faults, which form the western and eastern margins, respectively, of the San Felipe fault zone (Kelley, 1954) or San Felipe graben (Kelley, 1977). These faults are part of a series of faults that offset the basalt flows underlying Santa Ana Mesa. There appears to be little net throw across the San Felipe graben, although the Luce fault has apparent down-to-the-east offset of 90–120 m (Soister, 1952; Kelley, 1977) and the Algodones fault has apparent down-to-the-west offset of 50–60 m (Personius and others, 1999). These relatively large offsets in the 2.4- to 2.6-Ma (Bachman and Mehnert, 1978; Smith and Kuhle, 1998) basalts of the San Felipe volcanic field indicate a history of recurrent movement that may have extended into the early Pleistocene (Wong and others, 1995; Machette and others, 1998; Personius and others, 1999). However, displacements on some or all of the faults on Santa Ana Mesa may be related to volcano-tectonic processes (Personius and others, 1999); the narrowing of the fault zone near the center of the volcanic field supports this inference (for example, van Wyk de Vries and Merle, 1996). If most of the displacement on faults in the San Felipe graben is related to basalt eruption, then earthquakes associated with these faults may have smaller magnitude than those associated with tectonic faults (Smith and others, 1996). Numerous eruptive centers (unit Tbc) in the volcanic field are aligned in northerly patterns that mimic the fault strikes, but these features do not appear to be controlled by mapped faults and thus may be related to older structures (Kelley and Kudo, 1978). ACKNOWLEDGMENTS The author thanks Jim Cole and Paul Williams for manuscript review and Amy Zoller for incorporation of map data into GIS. The author also thanks the people of Santa Ana Pueblo for permission to conduct mapping on tribal lands. DESCRIPTION OF MAP AND SUBSURFACE UNITS [Surficial units are shown on map only if estimated to be at least 1 m thick. Colors of unconsolidated sediment are based on visual comparison of dry samples with Munsell soil color charts (Munsell Color, 1994). Soil-horizon designations and descriptive terms follow those of Birkeland and others (1991) and Birkeland (1999)] Qf Artificial fill (historic)—Locally derived and imported aggregate materials used for construction purposes. Used for highway fills along access road to old Santa Ana Pueblo, for a dike protecting old Santa Ana (Tamaya) Pueblo from Jemez River, and to divert an arroyo that previously flowed through eastern part of old Pueblo. Includes engineered fill at Jemez Canyon Dam and overflow spillway to south of dam. Unvegetated to sparsely vegetated to revegetated; no soil development. Thickness 1–30 m ARROYO ALLUVIUM Qalh Active channel alluvium (historic)—Light-yellowish-brown to brown (10YR 6–7/4), fine to coarse sand, silty sand, pebbly sand, and less common sandy pebble, cobble, and boulder gravel; poorly to moderately sorted, massive to well bedded, with local crossbedding; sand is poorly sorted to well sorted, fine to coarse grained, subrounded, and lithic and feldspathic in composition. Gravel clast compositions reflect local geologic units exposed in drainage area. Commonly forms channel fills and bars. Confined to present arroyo channel floors and bed of Jemez River. Unit commonly includes small areas of young eolian sand (unit Qesy). Sparsely vegetated (seasonal inundation) to unvegetated; no soil development. Thickness 1 to >5 m Qaly Younger arroyo alluvium (Holocene)—Light-yellowish-brown to light-gray (10YR 6–7/4), fine to coarse sand, mud, silty sand, pebbly sand, and sandy pebble, cobble, and boulder gravel; poorly to moderately sorted, massive to well bedded, with local crossbedding. Gravel clast compositions reflect local geologic units exposed in drainage area; clasts are chiefly reworked from underlying Santa Fe Group rocks, which primarily are derived 2 from source areas to northwest (Sierra Nacimiento and Jemez Mountains); common lithologies include Precambrian pink granitic rocks, petrified wood, Pedernal Chert Member of Abiquiu Formation, Paleozoic chert and limestone, Mesozoic sandstone, and intermediate to mafic volcanic rocks. Gravels commonly form 0.5- to 1-m-thick, channel-shaped or lenticular beds. Unit underlies low terraces along major arroyos and Jemez River, 2–8 m above adjacent channels. Unit commonly includes small areas of younger eolian sand (unit Qesy). Sparsely vegetated. Some low terraces along major arroyos contain charcoal-rich hearth sites. Soil development is minimal, usually with only minor oxidation, thin A horizons, and stage I Bk horizons. Thickness 1–5 m Qalo Older arroyo alluvium (Holocene to lower(?) Pleistocene)—Light-brown to light-gray (10YR 6/4–6), fine to coarse sand, silty sand, pebbly sand, and sandy pebble, cobble, and boulder gravel; poorly to moderately sorted, massive to well bedded, with uncommon crossbedding. Gravel clast compositions reflect local geologic units exposed in drainage area; in deposits south of Jemez River, clasts are chiefly reworked from underlying Santa Fe Group rocks, which primarily were derived from outcrops to northwest (Sierra Nacimiento and Jemez Mountains); common lithologies include pink granite, petrified wood, Paleozoic limestone and brown chert, Mesozoic sandstone, Pedernal Chert Member of Abiquiu Formation, basalt, intermediate volcanic rocks, and fragments of petrocalcic soil; clasts north of Jemez River are chiefly basalt.