Frozen River formation, Crystal Cave, Black Hills, SD, circa 1930

About this postcard

The view looks into a formation called the Frozen River, a mass of pale calcite inside Crystal Cave. Dark blue-black rock fills the top of the frame, a warm ochre-to-orange body of mineral sits at center, and white and grey granular textures spread across the lower and left portions. The crop is tight enough that the formation reads almost as an abstract pattern of color and grain. Crystal Cave is one of the limestone show caves in the Black Hills outside Rapid City, and the printed description makes the usual commercial pitch: electrically lighted passages, 1,600 rooms explored, 22 miles of paths, and a ranking of third among American caves behind Carlsbad Caverns and Mammoth Cave. Such rankings were promotional claims, but they show how cave operators competed for the motor tourists who began reaching the Hills in growing numbers in the 1920s and 1930s.