These data were collected using field portable (handheld) X-ray fluorescence (pXRF) equipped with a 4-watt Ta/Au X-ray tube. Samples of surficial alluvium, rock, and archived drill cuttings from monitoring wells in the western part of the Mojave Desert, 60 to 210 kilometers (km) northeast of Los Angeles, California, were measured using as part of an investigation of naturally-occurring trace elements dissolved in groundwater. Surficial alluvium samples were collected from small stream channels draining distinct geologic units, or from previously mapped river deposits, and generally consisted of silt, sand, and granules to small pebbles. Twigs and other detritus were removed prior to measurement. Rocks were collected from outcrops or from colluvium eroded from nearby outcrops and were broken to expose fresh surfaces whenever possible. Measurements were made on 180 samples of alluvium and rock, and archived drill material (cuttings) from 24 monitoring well sites, located over an approximately 14,300 square km area between March 2015 and May 2018.
Measurements on National Institute of Standards and Technology (NIST) and U.S. Geological Survey standard reference materials (available in a separate child page associated with https://doi.org/10.5066/P9CU0EH3) indicated the pXRF was sufficiently accurate for selected trace elements for the intended purpose of the dataset. Standard reference material indicated a need to adjust instrument beam times to optimize measurements of chromium. Measurements on a silica dioxide blank showed consistent clean (few to no measurable elements) data.