Figure 1.

Map of Yellowstone National Park showing hydrothermal areas sampled and locations of physiological sites. Hydrothermal areas are numbered alphabetically: 1, Calcite Springs; 2, Crater Hills; 3, Obsidian Pool Area; 4, Heart Lake; 5, Imperial Geyser Basin; 6, Lone Star; 7, Rabbit Creek; 8, Sentinel Meadows; 9, South of Sylvan Springs; 10, Sylvan Springs; 11, Washburn; 12, White Creek. Physiological samples, represented with open circles, in order from Northwest to Southeast are Bijah Spring, Nymph Creek, Dragon Spring, and Perpetual Spouter.