The proposed project is a geoarchaeological investigation for the Eureka Slough Bridges Replacement project. The purpose of the investigation is to gather data to inform the level of future studies needed for the bridge replacement project. The existing bridges are located approximately at post mile 79.78 on U.S. Highway 101 in Humboldt County. Core samples would be taken from 18 of 26 proposed locations adjacent to northbound U.S. 101 from post mile 79.4 to post mile 80.0 and southbound U.S. 101 from post mile 79.5 to post mile 80.0. A professional drilling crew would collect core samples of subsurface deposits using either a hollow-stem auger or a hydraulic push-tube device from areas accessible by a coring rig. Coring would be conducted at least 20 feet away from the fog line, 15 feet away from road shoulder, and 10 feet away from any known underground utility or structure. Each core would be pushed to a depth of nine meters or more below surface and would be stored in 1.2 to 1.5-meter-long and 4.7 centimeter in diameter or larger hard plastic liners for transport to a lab where they would be opened, examined, described, and subsampled. A Humboldt County drilling permit would be obtained for the coring work. All work would take place within Caltrans right of way. Biological, cultural, and traffic handling analysis have been completed.