With Parametrix and SCJ Alliance, HRA conducted archaeological and architectural investigations to aid the Washington State Department of Transportation (WSDOT) in improving the I-5 corridor between the Gravelly Lake Drive interchange (Exit 125) and the Mounts Rd. interchange (Exit 116). The project was subject to approval by the Federal Highway Administration (FHWA), was located on federal lands managed by Joint Base Lewis-McChord (JBLM), and was defined as a federal undertaking; therefore, compliance with Section 106 of the National Historic Preservation Act (NHPA) was required. HRA worked closely with the project team, JBLM staff, and WSDOT to define the area of potential effects, conduct archival research, and prepare a methods memo before conducting extensive archaeological investigations (33.8 acres of JBLM) and architectural and landscape inventories (17 buildings and 1 arboretum). HRA assessed the project for potential effects on National Register of Historic Places (NRHP)-eligible resources, including those within the Fort Lewis Garrison Historic District. Through consultation with JBLM, the Washington Department of Archaeology and Historic Preservation (DAHP), and the affected Tribes, the project was determined to have no adverse effects on cultural resources.