Geomorphology and Soils of First Order Watersheds in Emory Oak Savannas of the Animas Valley, New Mexico.

Twelve watersheds in the Peloncillo Mountains of southwest New Mexico have been monitored for seven years to study seasonal prescribed burning.  These watersheds are grouped in four blocks, each consisting of a cool-season burn, a warm-season burn, and a control watershed. Elevations range from 1,640 to 1,704 m. The watersheds (WS) range in size from 8 to 36 ha, with six (WS A through G) on the south side of Whitmire Ridge and other six (WS H through N) on the north. Channel lengths range from 720 to 1,020 m with a mean of 1,020 m, and channel slopes are between 2.5 and 7%. Channel types are mostly A1, A2, A3, and A4; with A1 channels ranging from 6% of WS A to 41% of WS K. Parent material in the study area is rhyolite, formed by ash flow tuffs and lava flows during the Oligocene.  The hillslopes adjacent to the Animas Valley are eroded and generally consist of colluvium-covered bedrock or exposed bedrock.  The resulting soils are about 0.4 m thick and consist of a 5 to 10 cm surface horizon of gravelly silt loam to gravelly clay loam and a 10 to 25 cm B-horizon of 40 to 70% gravel-sized clasts.  The NRCS soil survey of this portion of Hidalgo County classified most of the soils as rock land with bedrock at 0 to 30 cm.  In this land type, 30 to 85% of the soil surface consists of exposed bedrock, stones, and cobbles.  The 1991 Ecosystem Survey conducted by the U.S. Forest Service also identified soils in this area of the  Peloncillo Mountains that are Typic Haplustalfs, Typic Haplustolls, Typic Haplustalfs, and Lithic Ustorthents. These soils support Emory oak (Quercus emoryi), Toumey oak (Q. toumeyi), alligator juniper (Juniperus depeanna), and redberry juniper (Juniperus coahuilensis).