In 1978, the late Denis Marchand launched a project to identify, sample, and analyze soil profiles from seven soil chronosequences in the Western United States. The resulting datasets were compiled as part of a series of reports titled "Soil Chronosequences in the Western United States". Early studies of soil formation highlighted several key factors that together determine the degree of soil pedogenesis, which include climate, organisms (including vegetation), topography, and parent material (Jenny H.; 1941; Factors of Soil Formation, a System of Quantitative Pedology; https://doi.org/10.2134/agronj1941.00021962003300090016x). A soil chronosequence is defined as a series of soils in which all soil-forming factors except time are similar, where time is represented by soil or landform age. This compilation of chronosequences included soils developed on a variety of landforms including alluvial fans, fluvial terraces, glacial moraines, and marine terraces. The estimated age of these soils was based on a variety of chronological dating tools specific to each chronosequence and values range from modern-aged samples to samples that are three hundred thousand years old. At the time preceding this work, it was becoming clear from the marine record that the variations in climate and terrestrial processes were extensive with a paucity of numerical dating techniques applicable to the geologic record. The ubiquitous nature of soils made this project of critical importance to a better understanding of terrestrial processes. These data were originally published in analog form by individual authors in the U.S. Geological Survey Bulletin 1590 series, which was edited by J.W. Harden. Here, data from the original bulletin series including location, land cover, horizon depths, field morphology, color, texture, particle size, bulk density, organic carbon, pH, cation exchange capacity, dithionite extractable iron, major element abundance, trace element abundance, inorganic carbon content, and mineralogy, are compiled together as a single dataset in digital form. In addition, we have also compiled scanned field notes and site photographs that are associated with these publications. Furthermore, the original samples that were collected and analyzed associated with this dataset for the Colorado, Cowlitz, Kane Fans, Merced, Rock Creek, and Ventura chronosequences have been archived via the U.S. Geological Survey Soil Sample Archive (https://doi.org/10.5066/P90KTZW4).

Thin loess deposits on the uplands of the southeastern Colorado Plateau have previously not been well studied. We sampled deposits and soils from trenches on Hatch Point mesa near Canyonlands National Park, Utah, and from two outcrops in Mesa Verde National Park, Colorado. At Hatch Point, the oldest buried unit yielded two OSL ages of 10,370 and 7,555 yr; the middle unit yielded 10 OSL ages from 6220 to 1385 yr; and the youngest unit has a single age of 1740 yr. At Mesa Verde, three loess units are preserved in the two outcrops we examined; six OSL ages range from 51 to 17 ka. At least one buried soil is present between two units with ages of about 50 and 40 ka. The ages of the loess units in both study areas correspond well with OSL-dated dune sands in Canyonlands National Park and with dune sands on Black Mesa, Arizona. Particle size distribution combined with chemical and magnetic data indicate that Hatch Point loess was derived mostly from nearby sandstone sources with a small component of far-traveled atmospheric dust, whereas Mesa Verde loess was sourced both from the nearby sandstone and the San Juan River and its tributaries.

Thin loess deposits on the uplands of the southeastern Colorado Plateau have previously not been well studied. We sampled deposits and soils from trenches on Hatch Point mesa near Canyonlands National Park, Utah, and from two outcrops in Mesa Verde National Park, Colorado. At Hatch Point, the oldest buried unit yielded two OSL ages of 10,370 and 7,555 yr; the middle unit yielded 10 OSL ages from 6220 to 1385 yr; and the youngest unit has a single age of 1740 yr. At Mesa Verde, three loess units are preserved in the two outcrops we examined; six OSL ages range from 51 to 17 ka. At least one buried soil is present between two units with ages of about 50 and 40 ka. The ages of the loess units in both study areas correspond well with OSL-dated dune sands in Canyonlands National Park and with dune sands on Black Mesa, Arizona. Particle size distribution combined with chemical and magnetic data indicate that Hatch Point loess was derived mostly from nearby sandstone sources with a small component of far-traveled atmospheric dust, whereas Mesa Verde loess was sourced both from the nearby sandstone and the San Juan River and its tributaries.

This point dataset contains geologic information concerning regolith thickness and top-of-bedrock altitude at selected well and test-hole locations in the Lower Gunnison River Basin in Delta, Montrose, Ouray, and Gunnison Counties, Colorado. Regolith-thickness data were compiled from lithologic logs of wells and boreholes reported by the Colorado Division of Water Resources, U.S. Geological Survey, and Bureau of Reclamation. Bedrock-altitude values were computed from the bedrock altitude raster dataset (bralt). The U.S. Geological Survey prepared this dataset in cooperation with the Colorado Water Conservation Board.

This point dataset contains geologic information concerning regolith thickness and top-of-bedrock altitude at selected well and test-hole locations in the Lower Gunnison River Basin in Delta, Montrose, Ouray, and Gunnison Counties, Colorado. Regolith-thickness data were compiled from lithologic logs of wells and boreholes reported by the Colorado Division of Water Resources, U.S. Geological Survey, and Bureau of Reclamation. Bedrock-altitude values were computed from the bedrock altitude raster dataset (bralt). The U.S. Geological Survey prepared this dataset in cooperation with the Colorado Water Conservation Board.

This data set is a digital soil survey and generally is the most detailed level of soil geographic data developed by the National Cooperative Soil Survey. The information was prepared by digitizing maps, by compiling information onto a planimetric correct base and digitizing, or by revising digitized maps using remotely sensed and other information. This data set consists of georeferenced digital map data and computerized attribute data. The map data are in a soil survey area extent format and include a detailed, field verified inventory of soils and miscellaneous areas that normally occur in a repeatable pattern on the landscape and that can be cartographically shown at the scale mapped. A special soil features layer (point and line features) is optional. This layer displays the location of features too small to delineate at the mapping scale, but they are large enough and contrasting enough to significantly influence use and management. The soil map units are linked to attributes in the National Soil Information System relational database, which gives the proportionate extent of the component soils and their properties.

The San Juan basin is a significant physical and structural element in the southeastern part of the Colorado Plateau physiographic province. The San Juan basin is in New Mexico, Colorado, Arizona, and Utah and has an area of about 21,600 square miles. The basin is about 140 miles wide and about 200 miles long. In the 1980’s and 1990’s, the San Juan basin was the focus of the U.S. Geological Survey's Regional Aquifer-System Analysis (RASA) study. Investigation of the San Juan structural basin began in October 1984 with an objective, among others, to define and evaluate the aquifer system. As part of this analysis, a multi-publication series of reports were produced as Hydrologic Atlas 720 (HA-720) that described on 1:1,000,000-scale maps the subsurface configuration and hydrogeology of the San Jose, Nacimiento, and Animas Formations (Levings and others, 1990; HA-720-A), the Ojo Alamo Sandstone (Thorn and others, 1990; HA-720-B), the Kirtland Shale and Fruitland Formation (Kernodle and others, 1990; HA-720-C), the Pictured Cliffs Sandstone (Dam and others, 1990; HA-720-D), the Cliff House Sandstone (Thorn and others, 1990; HA-720-E), the Menefee Formation (Levings and others, 1990; HA-720-F), the Point Lookout Sandstone (Craigg and others, 1990; HA-720-G), the Gallup Sandstone (Kernodle and others, 1990; HA-720-H), the Dakota Sandstone (Craigg and others, 1990; HA-720-I), and the Morrison Formation (Dam and others, 1990; HA-720-J). This digital dataset contains spatial datasets corresponding to the contoured subsurface maps produced by the U.S. Geological Survey's Regional Aquifer-System Analysis (RASA) San Juan basin study. The data define the elevation, thickness, and extent of principal stratigraphic units of the basin. The digital data describe the following stratigraphic units: the San Jose Formation, the Ojo Alamo Sandstone, the Kirtland Shale and Fruitland Formation, the Pictured Cliffs Sandstone, the Cliff House Sandstone, the Menefee Formation, the Point Lookout Sandstone, the Gallup Sandstone, the Dakota Sandstone, and the Morrison Formation. Digital data for each unit are contained in individual features classes within a geodatabase (also saved as individual shapefiles). Feature classes have a single attribute, either elevation or thickness, that represents the contoured value. Contoured values are given in feet, to maintain consistency with the original publication, and in meters.