Niland Geyser is a moving mud pot near the Salton Sea in California, not a true geothermal geyser but a cool, carbon-dioxide-driven spring formed around 1953 in geologically unstable ground near the San Andreas Fault system. Known as W9 or the Slow One, it is exceptional for shifting across the landscape, likely because gas rises through fractured sediment and a tilted channel drives sideways migration. Its movement accelerated sharply after 2015, creating a deep basin and threatening rail lines, highways, pipelines, and fiber-optic cables. Costly engineering efforts repeatedly failed to stop it, making it one of California’s most unusual and dangerous active ground hazards.