Abstract To assist U.S. Air Force archaeologists study and preserve cultural sites associated with early Native American inhabitants of the Nevada Test and Training Range, we have determined the late Pleistocene environments of nine playas on the range from surface deposits around the playas. Based on shoreline features such as barrier bars, wave-cut benches, and beach gravel deposits, the playas of Mud Lake, Gold Flat, and Kawich Lake contained pluvial lakes. Based on fossils, palustral clay sediments, paleospring, and seep deposits, the playas of Stonewall Flat, Indian Springs Valley, and Three Lakes Valley contained extensive wetlands. Two playas in Cactus Flat and one at Dog Bone Lake contain none of these surface deposits and are interpreted to have hosted seasonal lakes and grassy meadows, based on modern analogs in the Pahranagat Valley. Radiocarbon dates from Mud Lake, Gold Flat, and Stonewall Flat indicate these environments existed up to the beginning of the Holocene ca. 10,000 years before present (yr B.P.) and would have provided resources of fresh water, fish and game, edible and medicinal plants, fuel, and materials for the construction of shelter. As changing climate conditions from 10,000–8000 radiocarbon yr B.P. forced the contraction and eventual disappearance of these lakes and wetlands, basins with larger surface water budgets probably furnished early inhabitants with useful resources after the pluvial features in the smaller basins had disappeared.

Analysis of geologic materials at the microscale—where we use the term “microscale” to refer to features resolved approximately by a hand lens—has proven to be a powerful strategy to maximize the information gleaned from limited samples, such as on Mars. However, discrimination between processes that leave behind similar traces requires enlightened comparisons to well-characterized analogs. We characterized and imaged several terrestrial analogs of materials produced by volcanic, hydrovolcanic, or cryovolcanic Martian processes at the hand lens scale, and then we produced a convenient tool for the community to access those data for comparisons. We report on the preparation of this Mars-focused image atlas (the Mars Analog Handlens-Scale Image Database), using as an example analog studies of particles deposited by the 1996 Skeiđarársandur jökulhlaup (a jökulhlaup is a subglacially generated outwash flood resulting in a sandur, or sheet of outwash sands and gravel). We imaged unconsolidated sediment particles in situ at about hand lens scale and documented their characteristics at six sites along the sandur. Average particle size and number of angular, very angular, and subangular particles decreased with distance from the source; the average sphericity of particles increased slightly; and the range of sphericity values present narrowed with distance. If observed in a region on Mars, this combination of characteristics would be one indicator that subglacially generated outwash flooding was the process responsible for deposition of sediment. The Mars Analog Handlens-Scale Image Database is searchable and can be found on the Geosciences Node of the Planetary Data System at http://an.rsl.wustl.edu/marsanalog/ .

We studied the composition and roundness of medium sand from 18 small beaches of Elba Island. Six are pocket beaches less than 100 m long; the longest is 1.3 km long. The drainage basins of streams that supply the beaches are all less than 25 km 2 ; most are less than 5 km 2 . Beach sands range widely in composition owing to diverse source terrane. For the various drainage basins, comparison of the outcrop areas of the different types of bedrock with the compositions of beach sand grains yields the following conclusions: (1) the relative area of granodiorite outcrop is accurately represented by the amount of quartz + feldspar + quartzofeldspathic rock fragments in all beaches, although plagioclase in beach sand is significantly reduced relative to K-feldspar; (2) the relative areas of outcrop of ophiolitic and limestone bedrock are accurately represented by beach sand in pocket beaches, but are only moderately represented (ophiolitic rocks) or poorly represented (limestone) in other beaches; (3) the relative area of outcrop of metamorphic rocks is poorly represented in beach sand (metamorphic rock fragments + polycrystalline quartz) except in one anomalous beach supplied in part by mine tailings; (4) the relative area of bedded chert outcrop is poorly represented in beach sand because bedded chert does not break down into sand-size grains; and (5) shale bedrock is not represented or is only marginally represented in beach sand. For Elba beaches in general, the order of increasing roundness of grains, and thus increasing rate of abrasion, is: quartz < plagioclase < K-feldspar and igneous rock fragments (quartzo-feldspathic) < serpentine < metamorphic rock fragments < carbonate rock fragments (CRFs). There are no significant differences in roundness with beach length for quartz, K-feldspar, or CRFs. There are also no significant differences in roundness for the same three grain types from beaches of different size drainage basins, which indicates there is no perceptible rounding of grains by streams. First-cycle monocrystalline quartz grains of medium sand are unrounded, although coarser grains show minor blunting of edges. The roundness of quartz, K-feldspar, and CRFs are all greater on the eastern, more protected part of the island. This reflects a significant proportion of recycled quartz and K-feldspar in the eastern beaches, but CRFs may undergo more rounding in beaches of low to moderate wave activity than in high-energy beaches.