Late quaternary geomorphology and geoarchaeology of a segment of the Central Mimbres River Valley, Grant County, New Mexico

Abstract

Two terraces, a modem floodplain, and alluvial fans were identified along a segment of the central Mimbres River Valley in Grant County, New Mexico. The oldest terrace, T2, is composed of one major depositional unit (1) and is capped by a welldeveloped soil (S 1) believed to be of Pleistocene age. The younger Holocene terrace, TI, is composed of three major depositional units (II, III, and IV) each capped with a soil (S2, S3, and S4 respectively). An Animas/Black Mountain Period site (ca. A. D. II 50 A. D. 1300) is believed to be associated with S3, and it is possible other sites, from Cliff/Salado to Mimbres-Mogollon, are buried in the fill of TI. A geomorphic map and generalized geologic cross section of the study area were also produced. Unfortunately, the question of the abandonment of the Mimbres River Valley at the end of the Classic Mimbres Period could not be answered because of the absence of reliable absolute ages for the deposits. Future research should focus on expanding the alluvial history to other segments of the Mimbres River and its side drainages, collecting radiocarbon samples to develop an absolute chronology, analyzing the soils and sediments in more detail to provide more information about depositional environments and duration of soil formation.