Bathymetric map of the West Thumb Basin, Yellowstone National Park

Bathymetric map of the West Thumb Basin showing numerous mapped active or inactive hydrothermal vent sites (small white circles) and sampled hot springs (white stars or larger white circles) and sediment cores (yellow diamonds).  The white-black line represents the 160,000-year-old West Thumb Caldera margin.  West Thumb Geyser Basin is near the southern end of extensive hydrothermal fields along the western shore of West Thumb Basin and includes two large (>100 m, or 328 ft, in diameter) landscape-shaping hydrothermal explosion craters immediately offshore at Evil Twin crater and at Duck Lake just west of West Thumb Basin.