CAMP SPRINGS -- Dan Walsh knew something was very wrong when he heard someone pounding on the back door.
Roused from sleep, Walsh stumbled to answer the noise. Standing outside his house early yesterday was a Prince George's County firefighter, who informed Walsh that his backyard, drenched by rain, had sunk about 10 feet and that he'd better get out before the house went with it.
"I saw the firefighter and the sinkhole at the same time, and I thought, 'Oh, my God,'" Walsh recalled a few hours later, puffing nervously on a cigarette. "I started shaking."
Walsh's was not the only house affected. The sinkhole ran the length of four properties, a jagged, undulating trench more than 200 feet long and at least 20 feet wide that might have seemed more likely in the aftermath of an earthquake. The swath cut the green, unfenced lawns and radically altered the topography of the area off Yorkville Road in Camp Springs, an unincorporated community south of Andrews Air Force Base.
Emergency officials who arrived shortly after 6 a.m. ordered the evacuation of three of the four houses, including Walsh's. Later, he was the only homeowner to be allowed back in because his house appeared to have suffered less structural damage than the two houses to the south. On those, officials posted bright orange signs that stated "This building is unsafe" and forbade entry.
In the back of one house, a carport with a late-1970s Mercury inside was perched at a precarious angle, its foundation cracked, the sunroom above it equally tilted and in danger of collapsing. Next door, the roof over a patio lay crumpled, its support columns snapped like twigs. Nearby, trees lay on their sides, their roots exposed to the driving rain.
Residents of the street, which is on a slight incline, said gravity had sent streams of water cascading into the backyards on the east side of Yorkville Road, making the ground unstable. Twelve years ago, they said, the same stretch of ground dropped after heavy rain, but only by about a foot.
"It settled a little bit, but you wouldn't think it would drop out of sight," said Walsh, 44, whose grandmother sold him the 1950s ranch-style house seven years ago.
On Sunday afternoon, before it began raining in earnest, Walsh had a cookout by himself by the picnic table in his backyard. Now, the picnic table is on the far edge of the chasm, unreachable, he said, "unless I walk through that ditch or build a bridge."
Walsh, who works for the Washington Suburban Sanitary Commission, said his neighborhood lacks storm drains, gutters and curbs that might direct rainwater away from backyards.
Charles W. Wilson, director of the Prince George's County Department of Environmental Resources, said geologists would study the lay of the land to determine the sinkhole's cause and would not hazard a guess until then.
Douglas Pfaff, 20, a student at Washington College in Chestertown whose aunt owns one of the evacuated houses and whose mother lives nearby, said officials had told residents after the previous land shift - which cracked a swimming pool and forced its removal - that there was no reason to worry about future geological failures.
"The county claimed no responsibility for this 12 years ago," Pfaff said, "and my guess is that they won't now."