Laboratory-based optical measurements for water samples collected from the Cache Creek watershed and settling basin, Yolo County, California

This data release documents measurements related to organic matter concentrations and characteristics in the Cache Creek Settling Basin in Woodland, California. Data files reported here provide full spectral results for absorbance and fluorescence analyses used for statistical modeling for proxy development. Commonly reported diagnostic absorbance wavelengths and fluorescence excitation-emission pairs contained in these spectra as well as a set of commonly calculated indices have been released to the USGS Water Data for the Nation (WDFN; formerly known as the National Water Information System (NWIS) database. The optical measurements reported here were collected to establish additional potential surrogates for mercury (Hg) and methylmercury (MeHg) concentrations and to provide more complete spectral information on temporal and spatial patterns of organic matter within the lake. Other water-quality data for the samples included in this data release are published in Alpers and others (2025) and Alpers and others (2026).