Data Series 283

Data Series 283

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In 1992, the National Park Service established, through its Inventory and Monitoring Program, a nationwide Level-1 Water-Quality Inventory process to obtain baseline water-quality information on key water bodies, to identify possible water-quality issues in national parks and monuments through the United States. Key water bodies are identified as those that are essential to the cultural, historical, or natural resource-management themes, or that provide habitats for threatened or endangered plants and animals. During June 2006, the U.S. Geological Survey (USGS) collected water samples from seven springs in the Pinnacles National Monument in support of the Level-1 Water-Quality Inventory program of the National Park Service (NPS). These samples were analyzed to obtain water-quality information regarding key water resources at the Monument.

Description of Study Area

Pinnacles National Monument encompasses 24,265 acres in the Gabilan Range of San Benito and Monterey Counties, California (figs. 1 and 2). It is bordered by the San Andreas Fault on the northeast and the Salinas Valley to the southwest (fig. 1).Most of the monument is underlain by volcanic rocks—rhyolite flows, breccias, and tuffs that have been moved about 195 mi northwest along the San Andreas Fault from the western Mojave Desert. These rocks have been fractured, faulted, and deeply incised by streams, producing valleys and ridges of high topographic relief. Rocky ridges are typically more than 1,000 ft above adjacent stream valleys. Parts of the Monument northeast from Chalone Creek are underlain by granitic fanglomerate—cemented sandy to bouldery sediments derived from a granitic source. Granitic rocks are exposed on the western and southeastern sides of the monument.

The area has a Mediterranean climate, with cold wet winters and hot dry summers. Average precipitation during 1948–2005 was 16.6 in. (, accessed September 12, 2005). Many streams in the monument are intermittent (drying up during the summer or fall) or ephemeral (flowing during and shortly after storms). Except for water from Bear Gulch Reservoir (fig. 2), and a few stock ponds, surface water is scarce; most of the monument’s water resources are ground water (Mary Cooprider, National Park Service, written commun., 2005). During the dry season, the source of streamflow in perennial stream reaches is ground water that is discharged to stream channels diffusely through channel boundaries, or through seeps and springs that flow into the channels. During the dry season, ground-water discharge is a primary source of water for wildlife in the Monument and provides habitat for plants, amphibians, and aquatic life.

Purpose and Scope

This data report summarizes the objectives, sampling plan, and sampling and analysis protocols used by the U.S. Geological Survey in conducting the level-1 baseline water-quality inventory of springs at Pinnacles National Monument. The objective of the report is to present water-quality information describing the general chemistry and isotopic composition of key water resources at the monument. The level-1 baseline water-quality inventory described in this data report focuses on perennial springs. NPS and USGS staff determined that water-quality samples should be collected from these springs and analyzed to determine the concentration of dissolved major ions, trace elements, nutrients, stable isotopes, and tritium. The National Park Service can use information in this data report to assess the current water quality of key springs and as a reference point for comparison of samples collected from future monitoring networks and hydrologic studies. The NPS can use the tritium and stable-isotope data in this report to derive some information on the recharge dates and evaporative history, respectively, of ground water in the monument. Establishing baseline water quality, ground-water age, and evaporative history of water from the springs provides information that will facilitate future study of ground-water-flow systems, stream-aquifer interaction, and wetlands. Ultimately, these data and future studies will improve the understanding of ground-water-flow systems that must be considered during the resource management decision-making process by NPS staff at Pinnacles National Monument.

The water quality of springs in the monument described in this report also is important from a critical habitat perspective. The California red-legged frog, listed as a threatened amphibian species by the Federal Government in 1996 (U.S. Fish and Wildlife Service, 2006), inhabits streams in Pinnacles National Monument. This amphibian species inhabits intermittent and perennial stream reaches (T. Leatherman, National Park Service, oral commun., 2005). The Pinnacles riffle beetle is found only in Pinnacles National Monument and surrounding area, and is ranked as an extremely endangered California endemic species in the California Natural Diversity Database. Additionally, Chalone Creek is habitat for an annelid worm that has not been identified elsewhere (S. Fend, USGS, oral commun., 2007). The sensitivity of the amphibian, beetle, and worm species to water availability, and possibly to water chemistry, requires that the Monument establish the baseline water quality of springs that are a primary source of stream water. This report provides that baseline information.

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