The Lewis and Clark Caverns Headquarters building, designed by National Park Service architect O. John Ballas and built by Civilian Conservation Corps (CCC) crews in 1938, is a model example of the Rustic or “Parkitecture” style. Drawing on Arts and Crafts design ideals, architects working in western parks in the 1920s and 1930s used native materials, low horizontal forms, and earth-tone colors reflective of the natural environment. In Montana, architects Robert Reamer, Kirtland Cutter, Gilbert Stanley Underwood, and Thomas McMahon led the movement in Glacier and Yellowstone national parks. Their designs translated well in this region where use of native log and stone was a natural extension of settlement building patterns. CCC crews, commissioned under Franklin D. Roosevelt’s New Deal jobs program, quarried lichen-encrusted limestone from Cave Mountain for the massive tapered stone porch piers, chimney, and fireplace. These elements, along with cedar shingles on the clipped gable roof, rough-sawn tongue-and-groove siding, and exposed-wood interior trusses show the skill and talent of Ballas and the ability of CCC crews to harmonize the built and natural worlds in this rugged mountain landscape.