A desiccation crack runs deep and wide south of Willcox playa.

Courtesy of Arizona Geological society

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The number of earth fissures spreading across Southern and Central Arizona due to excessive water pumping is approaching 300, a top state geologist said Monday.

The Arizona State Geological Survey's office released maps showing that earth fissures are proving an increased safety risk to homeowners, as development expands into areas where fissures date back to the 1940s or '50s and in some cases to the 1920s.

Authorities have warned for decades that continued land subsidence from groundwater pumping can open up huge fissures. The warnings have increased in intensity in recent years as more homes are built atop old fissures, particularly in rapidly growing Pinal County between Tucson and Phoenix.

So far, Arizonans are lucky that fissures haven't swallowed any homes, said Lee Allison, the survey's director and state geologist. But when a fissure opened up overnight in a Queen Creek area neighborhood two summers ago, it could have caused a home to collapse if it had opened directly under the home, he said.

"When we saw something open that catastrophically, when we see it can happen like that with a heavy rain, someone could have gotten hurt," Allison said.

By mapping and publicizing the fissures and working with local governments to find ways of dealing with them, the state is hoping to avoid a repetition of a collapse of homes in North Las Vegas, Nev., in the 1980s.

Home-building on earth fissures in that area's Windsor Park development forced North Las Vegas to pony up $14 million to buy up homes that in some cases were torn in half, according to a paper presented at a 2005 geologists' convention in Las Vegas. Scores of residents of North Las Vegas were forced to move from their homes after years of fruitlessly repairing twisted homes, schools, fences, roads and pipelines, said the Nevada Bureau of Mines and Geology.

In Arizona, the geological survey is zooming in for more intense study of 22 areas, picked for their rapid development potential, high fissure numbers and history of land subsidence. The subsidence, directly traced to massive groundwater pumping that outpaces recharge, has grown so intense in some areas that the ground compacts and ultimately collapses.

Pinal County has 12 fissure study areas, followed by Maricopa County with six, Cochise County with four and Pima County with one, in the Marana area. The survey estimates that the four counties have a total of 200 to 300 fissures.

"But boy, it's a squishy number," Allison said. "The reason is that the fissures are discontinuous, with branches splaying off of them. You follow one along the ground, it starts to die off and another few feet it starts up again."

One to 5 feet wide and 5-20 feet deep when they first appear, the fissures can be much deeper and longer — hundreds of feet deep and thousands of feet long — under the surface, said the survey. Heavy rains can soften the ground, however, which allows it to cave into the underlying fissure and can erode the fissure's sides, enlarging the fissure into a gully, the society's report said.

"Many fissures are spectacular open cracks that are immediately obvious even to the untrained eye," the report said. "Others are old and eroded, and look like washes, or have mostly filled with sediment."

Joan Etzenhouser of the Queen Creek area first thought the cracks on her property were "just part of the landscape" when they started to appear in 2004 and 2005, one to two years after she moved into the home.

Then, in August 2005, heavy rains left behind openings in three fissures, one running under her home and all three running across a wash.

Etzenhouser is suing the real estate agent and family that sold her and her husband the home on the grounds that they didn't disclose the fissure problem.

"I'm angry. I'm frustrated. I feel like I trusted people … the owner that sold me the home had to have known, known that there were weird things on this property other than scorpions and coyotes," said Etzenhouser, who lives on 3.3 rural acres.

Realtor John Richins, who represented the family that sold this home, declined to discuss the suit except to say that there were no fissures at the time the ground was sold: "I'm 66 years old. I've been a Realtor 25 years and I've never been sued in my life until now."

One and one-half miles to the north of that home, the same heavy rains of August 2005 had left behind a gully more than 15 feet deep and 9 feet wide that had swallowed a good part of a homeowner's front yard, Allison and another geologist wrote in an August 2006 article.

In another incident, a huge desiccation crack — which looks like a fissure but has a different origin — opened up last summer on private, vacant land just west of Kansas Settlement Road about 20 to 22 miles south of Willcox.

The crack, 100 feet long, 40 to 50 feet wide and 30 to 40 feet deep, and others of its kind are formed when soil close to the ground surface dries and shrinks.

The owner of the land filled the crack in three or four months ago, said Jackie Watkins, Cochise County's flood-plain manager.