Some Queen Creek area residents are bracing for what could be a destructive monsoon - but it's not flooding they worry about.

It's the earth fissures.

Slideshow: Rain aggravates fissures

Video: Queen Creek owner talks about her troubles with fissures

SPECIAL REPORT: Buyers beware, does your area have fissures?

Click to view an interactive graphic

As rain bombarded the semi-rural area late last week, large chasms opened near homes and roads, and again cracked the ground near a corral where a horse died after falling into a fissure last summer.

One crack, which opened along the edge of Queen Creek's Goldmine Mountain Equestrian Estates, exposed wiring and irrigation lines.

With the science surrounding fissures still developing, geologists can't say how far or deep the cracks reach.

Local activist Silvia Centoz has made it her mission to remind people of the potentially dangerous cracks and has renewed interest during the monsoon.

While walking in a Pinal County field on Wednesday, Centoz points out numerous cracks, ones that have grown in just days since the last rain.

"Look there are ATV marks - they've ridden right over fissures," she said while pointing to the ground.

She worries about children, animals and people who own property in the area because of the potential for injury and destruction.

"People need to understand that what they've interpreted as gopher holes are anything but," she said.

Pinal County resident Joan Etzenhouser, who recently had her property devalued 60 percent because of fissures, watched even more small holes turn into cracks.

Her property in the San Tan Foothills is said to have a system of fissures - one that runs underneath her house and another that traverses her driveway

New holes have formed and "everything's gotten bigger," she said. "It's scary."

She said she may have to fill or put fences up around some of the larger cavities for safety.

With more rain likely she said she's waiting to see what's next.

"The hazards are getting worse, that's what I'm worried about," she said.

Fissures are subsidence cracks caused by the overharvesting of groundwater. As the earth subsides, cracks form and are often exposed during heavy rain. State geologists have said that three-quarters of the state's earth fissures are in Pinal County and maps released this spring show fissures in the San Tan area and Queen Creek.

State geologist Todd Shipman, who was mapping fissures in the Picacho area Wednesday as part of a statewide project, said people should be mindful of the fissures.

"These cracks are really subtle, they can be a centimeter wide, but once water starts flowing into them they open up and flare out at the very top," Shipman said. "Some fissures can be up to 25 meters deep (roughly 75 feet)."

Shipman said people are encouraged to call the State Geological Survey at (520) 770-3500 to report fissures they've found.

"After heavy rains they should go around and make sure nothing's opening up," he said. "As for precautions, there's nothing you can really do other than be mindful and look at the map."

Fissure maps are available on the state geological service Web site at www.azgs.az.gov.

"We worry about someone not knowing and driving their cars across there..." he said. "It could definitely injure someone or destroy property."