Desert Project - An analysis of aridland soil-geomorphic processes

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The Desert Project—An Analysis of Aridland
Soil-Geomorphic Processes
Bulletin 798
H. Curtis Monger, Leland H. Gile, John W. Hawley, and Robert B. Grossman1
Agricultural Experiment Station • College of Agricultural, Consumer and Environmental Sciences
Department of
Plant and Environmental Sciences
INTRODUCTION
In August 1957, R. V. Ruhe and L. H. Gile moved to
Las Cruces, NM, to begin the Desert Soil-Geomor-phology
Project (the Desert Project) of the U.S. Soil
Conservation Service (SCS) (Appendix A). At that time,
little was known about soils in arid and semiarid regions
of the American Southwest away from alluvial valley
floors. This study was undertaken to learn more about
the morphology, classification, genesis, and occurrence
of desert soils and their relation to late Cenozoic land-scape
evolution, and to assist in understanding, classify-ing,
and mapping soils in similar geomorphic settings
elsewhere. The hallmark of this investigation was the
integration of classic pedologic and geologic approaches
in the study of a desert and semidesert soil-geomorphic
system. Another distinctive feature of the project was
the large number of formal and informal field seminars
held in the study area. Hundreds of scientists and stu-dents
from many parts of the world participated in these
programs, and a series of field trip guidebooks evolved
over a period of 46 years (1961–2007). Desert Project
research between 1957 and 1972 is described in detail in
Hawley (1975a, 1975b), Gile and Grossman (1979), and
Gile et al. (1981).
Guy D. Smith, Director of the SCS’s Soil Survey
Investigations Division, provided overall administrative
and technical supervision of the Desert Project until
his retirement in 1972. R. V. Ruhe conducted initial
geologic and geomorphic studies as a full-time partici-pant
from August 1957 to August 1960, and during
short-term assignments several times a year through
1965 (Ruhe, 1967). F. F. Peterson was responsible for
geomorphic investigations and some aspects of soils
research from 1960–1962. J. W. Hawley conducted
Introduction....................................................................... 1
Setting......................................................................................................3
Physiography........................................................................................3
Climate................................................................................................4
Vegetation............................................................................................6
Landforms and Stratigraphy............................................... 6
Parent materials, basins, and river valley...................................................6
Cenozoic stratigraphy and the ancestral Rio Grande.................................6
Hydrogeology...........................................................................................10
Atmospheric Additions....................................................... 10
Geomorphic Surfaces and Morphostratigraphic Units....... 10
Geomorphic surfaces as a mapping concept..............................................10
Morphostratigraphic units as a mapping concept......................................11
The valley border stepped sequence......................................................11
Effect of landscape dissection on geomorphic surfaces and soils................11
Constructional surfaces versus structural benches.....................................15
Paleoclimate........................................................................ 17
Late Quaternary climates..........................................................................17
Cyclic entrenchment of the Rio Grande....................................................17
Cyclic sedimentation and buried soils of the fan piedmont.......................17
The Gardner Spring radiocarbon site....................................................17
Polygenetic soils........................................................................................23
Soil Chronology................................................................. 23
Land survey notes.....................................................................................23
Buried charcoal.........................................................................................25
Radiocarbon ages of pedogenic carbonate.................................................25
Radiocarbon differences between carbonate and organic carbon...............26
Volcanic ash..............................................................................................30
Paleontology.............................................................................................30
Relative ages based on pedogeomorphic tracing and soil development......30
Soils and Soil-Geomorphic Relations................................. 30
Soil horizons and conventions..................................................................30
Soil taxonomy...........................................................................................32
Horizons of carbonate accumulation........................................................32
Origin..................................................................................................32
The morphogenetic sequences and stages of carbonate accumulation...32
Effect of increasing precipitation on development of the sequences......35
The calcic and petrocalcic horizons......................................................36
Micromorphology of carbonate accumulation......................................37
The K horizon......................................................................................37
1Respectively, Professor, Department of Plant and Environmental Sciences,
New Mexico State University, Las Cruces; Soil Scientist (retired), Natural
Resources Conservation Service; Senior Environmental Geologist (retired),
New Mexico Bureau of Mines and Mineral Resources; and Soil Scientist
(retired), Natural Resources Conservation Service.
Table of Contents