New Mexico Geological Society Downloaded from: http://nmgs.nmt.edu/publications/guidebooks/30 Geomorphology of Espanola Basin Vincent C. Kelley, 1979, pp. 281-288 in: Santa Fe Country, Ingersoll, R. V. ; Woodward, L. A.; James, H. L.; [eds.], New Mexico Geological Society 30th Annual Fall Field Conference Guidebook, 310 p. This is one of many related papers that were included in the 1979 NMGS Fall Field Conference Guidebook. Annual NMGS Fall Field Conference Guidebooks Every fall since 1950, the New Mexico Geological Society (NMGS) has held an annual Fall Field Conference that explores some region of New Mexico (or surrounding states). Always well attended, these conferences provide a guidebook to participants. Besides detailed road logs, the guidebooks contain many well written, edited, and peer-reviewed geoscience papers. These books have set the national standard for geologic guidebooks and are an essential geologic reference for anyone working in or around New Mexico. 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One printed copy of any materials from the NMGS website or our print and electronic publications may be made for individual use without our permission. Teachers and students may make unlimited copies for educational use. Any other use of these materials requires explicit permission. This page is intentionally left blank to maintain order of facing pages. New Mexico Geol. Soc. Guidebook, 30th Field Conf., Santa Fe Country, 1979 281 GEOMORPHOLOGY OF ESPANOLA BASIN VINCENT C. KELLEY Department of Geology University of New Mexico Albuquerque, New Mexico 87131 INTRODUCTION early Laramide uplifts, thus producing downwarping and The Espanola basin is one link in a chain of six or seven extensional faulting that became the Rio Grande rift. At the similar basins which comprise the Rio Grande rift or depres- time of basin subsidence, uplifts such as the Nacimiento, sion and are followed by the Rio Grande from southern Colo- Jemez and Brazos were present on the west and northwest. On rado to southern New Mexico. In many respects, it may be the east, there was a more subdued and mature version of the considered the type basin owing to the fact that the Neogene Laramide Sangre de Cristo uplift, and its margin lay five to ten Santa Fe Formation or Group has its type sections in the miles (8 to 16 km) west of its present position. It was from Espanola valley (Baldwin, 1956; Bryan, 1938; Cabot, 1938; these sources that much of the Santa Fe sediments of the Galusha and Blick, 1971; Hayden, 1869; Smith, 1938). Physio- subsiding Espanola basin were derived. graphically, the basin is rimmed by alternating ranges and During Miocene and early Pliocene, older sedimentary and plateaus (fig. 1). The Rio Grande, which is axial to the basin, crystalline sources were augmented by volcanics which comes in through a plateau gorge on the north and goes out erupted in the Jemez, Brazos and a Sangre de Cristo area some through a gorge on the south. On the west, the basin boundary distance northeast of Espanola basin. Sedimentation continued is straddled by the great Jemez Mountains volcanic pile. On as the basin subsided, and in particular, as the Sangre de Cristo the northwest, the basin is bounded irregularly by the north- source area slowly tilted upward. Although the basin had northwest-trending Brazos and Tusas ranges. The northern depositional axes generally along the Rio Grande and Rio boundary is the irregularly eroded edge of the Taos Plateau. Chama courses, the major subsidence and uplifting of On the east, the boundary is the Sangre de Cristo Range trend- borders did not come about until after most of the presently ing southward from the Picuris Mountains and terminating preserved Santa Fe sediments were deposited. The actions about 12 mi (19 km) south of Santa Fe. The southern end of involved principally broad uptilting of the eastern side of the the basin is marked irregularly by the cluster of porphyry and basin where original depositional dips of a degree or two were volcanic Cerrillos Hills and the northern rim of Galisteo River increased widely to 5-10 degrees. Locally along faults and valley, an eastern tributary of the Rio Grande (fig. 2). The along the monoclinal flexure at the Sangre de Cristo margin, southwestern margin is taken at the La Bajada fault escarp- dips are now up to 25-30 degrees. It was also a time of much ment and the Cerros del Rio volcanic hills. Both the valley and normal faulting, and displacements appear to have been at least the basin are centered about the confluence of the Rio Grande several hundred feet in many places. This period of late and its principal tributary, Rio Chama, which drains into the Pliocene tilting and faulting is widely present along the rift and basin from sources along northeastern areas of the Colorado in the adjoining eastern Rockies (Tweto, 1978). The Plateau. These rims are fed in the basin area by numerous deformation was a form of Basin and Range tectonics. For this tributaries from the surrounding mountains. Notable among late Pliocene deformation, the term "Santa Fe disturbance" is these are: El Rito and Ojo Caliente on the northwest; Em- proposed as a culmination to the overall Rio Grande rifting. budo, Truchas, Santa Cruz, Pojoaque-Tesuque and Santa Fe Following the Santa Fe disturbance, widespread tectonic on the east; and Santa Clara and Frijoles on the west. Altitudes stability set in. Erosion of upturned beds and elevated scarps along the Rio Grande through the basin are 6,050 ft (1,845 m) was relatively rapid and pedimentation spread widely about on the north down to 5,300 ft (1,616 m) on the south. Alti- the basin. tudes in the surrounding mountains range up to 13,101 ft (3,994 m) in the Sangre de Cristo Range; 11,551 ft (3,522 m) PEDIMENTS in the Jemez Mountains; and 8,602 ft (2,623 m) in the Brazos Nature and Distribution and Tusas mountains. There are several pediments in the Espanola basin, but by far the most significant is the Ortiz surface, first named by BASIN DEVELOPMENT Bryan (1938, p. 215). A few higher and older surfaces of local In order to understand the origin of the existing extent occur around the Jemez, Nacimiento, Brazos and landforms, it is necessary to review development of the Picuris areas (fig. 1), but evidence that they were widespread is Neogene basin. Prior to basin development, the area was not convincing. A local lower surface (Santa Cruz) that may probably a part of the eastern margin of the Colorado Plateau have been a pediment is suggested by numerous concordant along its junction with the Colorado-New Mexico orogenic remnants along the eastern side of the basin (see below). The Rockies (Kelley, 1979b). The southern part of the Espanola Ortiz surface and its equivalents along the Rio Grande region area appears to have been occupied by a portion of the most certainly were recognized by geologists of the earliest Galisteo Eocene basin and the northern parts were highlands surveys in the Southwest. Johnson (1903, p. 174-175) was (Gorham and Ingersoll, this guidebook). Regional uplift of possibly the first to note and describe this surface around the much of New Mexico during late Eocene and most of Ortiz Mountains, and Yung and McCaffery (1903, p. 353) Oligocene caused widespread erosion of the region. This described the gold-bearing placer gravels around the San Pedro seemingly long period of epeirogenic stabil- ity was then (Tuertos) Mountains. Lee (1907, p. 11, 19) referred to the followed by a change to crustal extension. As a result, the high gravels as "mesa gravels." Stearns (1953, p. 476-477) Colorado Plateau margin foundered along the roots of the 284 KELLEY named the gravels overlying the Ortiz surface Tuerto Gravel in or compound surfaces which may be arched or fanform and be the San Pedro area (Kelley and Northrop, 1975, p. 70). The at different altitudes along the bases of successive mountain term "Ortiz gravels" also has been used, and many geologists spurs and canyons. More than two-thirds of the original use "Ortiz surface" for the undissected tops of the covering surface has been removed (fig. 1) and it is not surprising, gravels as well as the cut surface at the base (Spiegel and therefore, that higher and lower parts may appear to be of Baldwin, 1963, p. 49). This practice arises from the fact that different ages. The modification of the sur- faces during the the pediment cover is commonly rather thin, and that near canyon cutting is discussed further below. rock fans at the head of pediments, the cover may be patchy. Ortiz Correlation and Reconstruction An additional problem is that at the bolson, playa or bajada end of the cover there may have been little or no interruption Figure 1 shows the surface outlines of the correlated Ortiz between uppermost Santa Fe and pediment covers.