For years, neighbors of a once vacant property in the San Tan area have warned prospective buyers about land fissures that lurk below.

View fissures map

Take a tour of the property with state geologist Todd Shipman

But foundations were recently poured and three homes are now rising from the ground on the patch of land located between Hunt Highway and Sun Dance Drive — an area neighbors and a state geologist says is known to have fissures.

Fissures are subsidence cracks caused by groundwater harvesting and are exposed during heavy rains. The science of fissures isn’t well-developed, but geologists are learning more all the time, Arizona Geological Survey geologist Todd Shipman said.

Shipman, the manager for a project to map every fissure in the state, confirmed three, and possibly more, fissures on the subdivided property in the San Tans.

Though there are fissures all over the Chandler Heights and San Tan area, Shipman he’s never heard of a home being damaged by one, and an engineering consultant for the homes being built maintains there are no fissures on the property where the homes are being built.

On a recent trip to the site, Shipman used a global positioning device interwoven with a geographic information system to map the fissures. He said his work was also looked at several visibly open cracks and defining locations using previous maps and aerial photographs.

“Everybody that works in that area knows about these fissures,” Shipman said. “If they don’t believe my mapping, they can look at earlier mapping.”

Tom Lang, who has lived on property adjacent to the under-construction homes for 28 years, said he has watched the fissures come and go with rain and has marked them by tying twine to bushes adjacent to the subsidence cracks. A few years ago, Lang also placed an iconic whitewashed tractor tire with a sign on his property warning “buyer beware” of the adjacent property’s fissures.

Lang said his main concern is for the people who plan to build homes — they need to investigate the possibility of fissures, he said.

“I don’t mind the houses going up, but what’s it going to be like when we get a real heavy rain and something falls in these cracks,” Lang said.

According to the Pinal County Assessor’s Web site there are several property owners with lots on the 40 acres — lot sizes ranging from 12.5 acres to 1.25 acres.

Shipman said he was asked by Pinal County about possible fissures on the property in March when someone wanted to develop there. He said he told county officials that there were fissures on the property.

“There are definitely people out there who have been doing this longer than me, but I can take you out there and show you the fissures,” Shipman said.

He said fissures on the property are difficult to track through historical aerial photographs because a gravel quarry used to be located there and neighbors say developers backfilled fissures there in the past.

“I think the real problem is if they build these buildings here and then our disclosure maps come out, they’re stuck with having to disclose the fact that there are earth fissures,” Shipman said. “There is an earth fissure right on the edge of where they graded. There is another earth fissure out there (in an undeveloped portion of the property) that is totally covered over.”

There is nothing to prevent people from building near fissures.

According to Pinal County records, three building permits have been approved on the property. Calls to two of the three owners listed on the permits were not returned. The third could not be found. More land in the area is listed for sale and calls to the real estate agency went unreturned.

“It’s folly to think that if you have a fissure and it stops right here at the surface, that there isn’t anything below it that just hasn’t made its way to the surface,” Shipman said. “It’s difficult for us to get a good handle on where they are, but there’s no doubt there are fissures there.”

Shipman said the worst damage caused by fissures was this summer, when a horse fell into an open fissure and died after monsoon rains.

“It’s not a matter of stopping all building. It’s a matter of making sure people know what they’re getting into and building in a manner that is making the house strong enough for the situation,” he said. “We can only hope that they’re trying to be responsible.”

Martin DeMarse, an engineering consultant for the three homes being built on the property, said they were responsible and a study was conducted showing no fissures on the site.

“They hired one of the most well-known geologists for fissures to make sure there are no fissures on the property,” DeMarse said. “The property owners did the proper due diligence to verify that there are no fissures on that property.”

DeMarse said he could not remember the name of the geologist.

But Shipman said the state’s next fissure map, due before the end of the year, will show fissures on the property, and the real problem will come when the homes are being resold.

“You invest so much into something and then if it’s got an earth fissure on it, it’s not a matter that it’s a real problem, it’s what people perceive as a problem,” he said. “If they feel they don’t want to invest because of that risk, the value goes down.”