(from the Express-News)
San Antonio fire and police officials evacuated 20 homes in a Northwest Side neighborhood Sunday morning, when a rapidly-growing sinkhole behind three houses pushed earth down a 30-foot hill and into two retaining walls that fissured and threatened to bury residences below.
While authorities were not sure why the ground had shifted behind houses in The Hills at Rivermist, agencies acted quickly to address the endangered homes near West Hausman Road and Loop 1604.
UPDATE: They are calling it a "slope failure." Apparently a huge retaining wall has given way.
UPDATE II: The Associated Press has picked up on the story.