Abstract Airborne dust suppression is of critical importance to military operations conducted in desert environments. Airborne dust is commonly generated in the desert by surface and near-surface operations during operational, testing, and training missions. Currently, there is no standardized procedure for testing dust suppressants, and the U.S. military lacks a specific test operations procedure (TOP) designed to provide realistic testing of the performance and durability of commercial products sold for dust abatement. The primary purpose of this study is to provide recommendations for the future development of a TOP for testing dust suppressants applied to desert soils. Recommendations were developed from the evaluation of a polyvinyl-based synthetic polymer as a dust suppressant, which was tested at four test intervals over a 19–week period in the late spring and summer of 2008 at the U.S. Army Yuma Proving Ground. The dust suppressant was applied at three separate test sites having different surface characteristics and soil properties ranging from loose, sandy gravel to gravelly sand, alluvial-fan soils to soft, sandy-silt, alluvial-plain soils. Each test site was subjected to a variety of traffic impact types consisting of an increasing number of cumulative passes by different vehicle types—including a low-flying helicopter, a light-weight armored tracked vehicle, and heavy-, medium-, and lightweight wheeled vehicles, plus pedestrian foot traffic. In addition to the sites of traffic impact, three types of control plots were concurrently tested to act as reference sites, as well as to evaluate the longevity of the suppressant, which included: disturbed and static (undisturbed) baseline plots and a static benchline plot. Surface soil and dust-suppressant physical properties were measured following each traffic impact in the form of shear strength and bearing capacity, plus dust-emission flux as measured by a Portable In Situ Wind ERosion Laboratory (PI-SWERL). Results from this study show that dust-emission flux and surface-strength measurements from a layout of control and traffic impact test plots provide a quantifiable and repeatable approach in measuring the efficacy of a dust suppressant for a TOP used by the U.S. Army.

Abstract Dryland channel networks share many similarities with channel networks in more humid regions, but they are also unique in having: extreme temporal and spatial variability in rainfall, runoff, and both hillslope and channel processes; poor integration between tributary and main channels; dominantly ephemeral or intermittent flow; and lack of equilibrium between process and form. Floods are likely to be particularly important in dryland channels, and riparian vegetation exerts a strong influence on channel processes and form. Land managers working in dryland channel networks particularly need to answer the following questions: What is stable? What is the role of disturbance? How do ecosystems depend on physical form and process? This paper explores methods for determining thresholds and resiliency within a channel network and suggests metrics that can be used to assess the condition of a channel segment or entire drainage network relative to management goals. The management metrics focus on flow regime, sediment supply, bed grain size, bedform configuration, width/depth ratio, bed gradient, channel planform, and extent and type of riparian vegetation. For each of these metrics, geological, historical, and systematic records can be used to define the natural range of variability for a particular channel form in the absence of direct land-use impacts. The range of variability present under land use such as military training activities can then be compared to the natural range to assess whether these activities are negatively affecting the dryland channel network. The Yuma Wash drainage in the Yuma Proving Ground, Arizona, is used as a case study.

The late Neogene section in the Salton Trough, California, and along the lower Colorado River in Arizona is composed of marine units bracketed by nonmarine units. Microfossils from the marine deposits indicate that a marine incursion inundated the Salton Trough during the late Miocene. Water depths increased rapidly in the Miocene and eventually flooded the region now occupied by the Colorado River as far north as Parker, Arizona. Marine conditions were restricted in the Pliocene as the Colorado River filled the Salton Trough with sediments and the Gulf of California assumed its present configuration. Microfossils from the early part of this incursion include a diverse assemblage of benthic foraminifers ( Amphistegina gibbosa , Uvigerina peregrina , Cassidulina delicata , and Bolivina interjuncta ), planktic foraminifers ( Globigerinoides obliquus , G. extremus , and Globigerina nepenthes ), and calcareous nannoplankton ( Discoaster brouweri , Discoaster aff. Discoaster surculus , Sphenolithus abies , and S. neoabies ), whereas microfossils in the final phase contain a less diverse assemblage of benthic foraminifers that are diagnostic of marginal shallow-marine conditions ( Ammonia , Elphidium , Bolivina , Cibicides , and Quinqueloculina ). Evidence of an earlier middle Miocene marine incursion comes from reworked microfossils found near Split Mountain Gorge in the Fish Creek Gypsum ( Sphenolithus moriformis ) and near San Gorgonio Pass ( Cyclicargolithus floridanus and Sphenolithus heteromorphus and planktic foraminifers). The middle Miocene incursion may also be represented by the older marine sedimentary rocks encountered in the subsurface near Yuma, Arizona, where rare middle Miocene planktic foraminifers are found.

Where the lower Colorado River traverses the Basin and Range Province below the Grand Canyon, significant late Pleistocene aggradation and subsequent degradation of the river are indicated by luminescence, paleomagnetic, and U-series data and stratigraphy. Aggradational, finely bedded reddish mud, clay, and silt are underlain and overlain by cross-bedded to plane-bedded fine sand and silt. That sequence is commonly disconformably overlain by up to 15 m of coarse sand, rounded exotic gravel, and angular, locally derived gravel. Luminescence dates on the fine sediments range from ca. 40 ka to 70 ka, considering collective uncertainties. A section of fine-grained sediments over a vertical range of 15 m shows normal polarity magnetization and little apparent secular variation beyond dispersion that can be explained by compaction. Aggradation on large local tributaries such as Las Vegas Wash appears to have been coeval with that of the Colorado River. The upper limits of erosional remnants of the sequence define a steeper grade above the historical river, and these late Pleistocene deposits are greater than 100 m above the modern river north of 35°N. Terrace gravels inset below the upper limit of the aggradational sequence yield 230 Th dates that range from ca. 32 ka to 60 ka and indicate that degradation of the river system in this area closely followed aggradation. The thick sequence of rhythmically bedded mud and silt possibly indicates settings that were ponded laterally between valley slopes and levees of the aggrading river. Potential driving mechanisms for such aggradation and degradation include sediment-yield response to climate change, drought, fire, vegetation-ecosystem dynamics, glaciation, paleofloods, groundwater discharge, and building and destruction of natural dams produced by volcanism and landslides.

Abstract This field guide describes a two-and-one-half day transect, from east to west across southern California, from the Colorado River to the San Andreas fault. Recent geochronologic results for rocks along the transect indicate the spatial and temporal relationships between subarc and retroarc shortening and Cordilleran arc magmatism. The transect begins in the Jurassic(?) and Cretaceous Maria retroarc fold-and-thrust belt, and continues westward and structurally downward into the Triassic to Cretaceous magmatic arc. At the deepest structural levels exposed in the southwestern part of the transect, the lower crust of the Mesozoic arc has been replaced during underthrusting by the Maastrichtian and/or Paleocene Orocopia schist.