Look up your property's hazards in the county's own maps

Where the maps are, and how to use them

There are two free tools. The Washington County Hazards MapServer, at agisprodvm.washco.utah.gov/arcgis/rest/services/Hazards/MapServer, holds the 24 county layers. The Utah Geologic Hazards Portal, at maps.geology.utah.gov/hazards, is the state survey's own viewer for the same study area. Open either, search your address, and turn on one layer at a time. Each hazard layer paints your parcel with a category code, and the code is what you write down. Hurricane City also keeps its own Special Study Maps for permits.

Flood: why there are three layers, not one

In January 2005, a Pacific storm dropped heavy rain on snowpack and the Santa Clara River widened to a hundred yards in places. Roughly 20 homes washed away and another 10 were damaged beyond repair. Washington County's Santa Clara River Master Plan puts the peak at about 6,200 cubic feet per second, roughly a 25 year event against a 100 year estimate near 13,000, and attributes the damage to large lateral erosion. Two facts should change how you read a flood map. The discharge "was less than expected for the 100-year flood." And "most destroyed homes were situated above the 100-year floodplain, leaving residents uninsured." The mechanism was stream bank erosion as the channel moved, not water rising over the banks.

That is why the county publishes an Erosion Hazard Boundary (layer 3) and a Flood Hazard Based on Geologic Deposits layer (4) alongside the FEMA layer (0). FEMA's map alone was not enough in 2005 and it is not enough now. Check all three, then the dam break inundation layers, 5 through 7, because Quail Creek and Sand Hollow sit upstream of a lot of houses. The plumbing connection is drainage: the first monsoon storm after a long dry spell lands on crusted, hydrophobic soil and is the riskiest moment of the year for a house's drainage and, as the next sections explain, for the soil under it.

Rockfall: the 40,000-gallon leak

The Utah State Hazard Mitigation Plan, Chapter 8, records it in one sentence: "At around 3:00 AM on January 19, 2013, a 12 x 9-foot boulder dislodged from sandstone within Foremaster Ridge and crashed into a house, seriously injuring a woman." The plan attributes the cause to a "40,000-gallon water leak associated with a house atop the ridge."

That is a state document, about St. George, linking an undetected residential water leak to a near-fatality. Special Study 127 says rockfall has "widespread favorable conditions" here and expects damage to increase with hillside development. If your parcel is inside the Rockfall Hazard layer (17), or you are the house on top of the ridge, a slow leak is not a water-bill problem. Check your meter with everything off; if the low-flow indicator moves in 30 minutes, something is running.

Soils: what the codes mean for your pipes

Expansive rock and soil (layer 19). Categories run Soil High (ESH), Moderate (ESM), Low (ESL), the same for rock, and Subsurface High. The local material is the blue clay of the Chinle Formation's Petrified Forest Member, an illite-smectite clay that swells wet and shrinks dry. It occurs in an arc across the St. George area and dips deeper toward the north, so it is a problem mainly where shallow. Documented damage includes cracked foundations and the outright demolition of condominium units on Bluff Street and the Knights Inn Motel. Expansive soils are 42.87 percent of Utah's classified problem soils. A pipe held rigid where it enters the slab and free in the soil takes every cycle of that movement as bending at the penetration.

Collapsible soil (layer 18). Categories HCS Very High through CSA, CSB, CSC, CSD. The survey's definition: soils "that have considerable strength when in a dry, natural state, but significantly settle due to hydrocompaction when wetted." In a neighborhood the wetting agent is almost always a leaking irrigation line, a failed service line, a downspout at the foundation or a broken sewer lateral. The loop runs leak, wetting, settlement, more pipe breakage, more leak. On collapsible ground, leak detection is foundation protection.

Gypsiferous rock and soil (layer 20). Gypsum dissolves, which opens voids, and sulfate attacks concrete. Under the ACI exposure classes, dissolved sulfate in water of 150 to 1,500 ppm is class S1 and 1,500 to 10,000 is S2; sulfate-resistant cement is required at S2 and above. St. George's own culinary water runs up to 451 ppm sulfate, inside S1 on the water column alone. Whether your footings or sewer bedding need a sulfate-resistant mix is a site soil test question, not a blanket St. George rule.

Caliche. Mapped as an adverse construction condition; the survey says it "can be very difficult to excavate." It shows up as a hard bearing shelf next to soft backfill under a sewer line, and as a bucket around a tree's roots. No primary source publishes typical depths for local caliche, and we will not either. What you can do is dig a test hole and fill it: the University of Arizona's field rule is that if the water drops at least four inches in four hours, drainage is adequate.

Piping and erosion (22) is subsurface erosion that can open a sinkhole under a yard or patio, triggered by the same concentrated water. Wind-blown sand (21) is unusual to see on a county hazard map at all, which tells you it matters here.

What soil movement does to a sewer line

A gravity sewer lateral needs a consistent quarter-inch of fall per foot. Differential soil movement of a fraction of an inch across one joint creates a belly, where water stands and solids collect, or an offset, the ledge roots grow into. A recurring "roots in the line" call here is often a soil problem wearing a root costume.

That matters when someone quotes you a repair. Neither pipe lining nor pipe bursting corrects a belly; the new pipe follows the old grade. A sagging line has to be dug, re-bedded and re-graded. If the map shows expansive or collapsible ground and the camera shows standing water, the honest quote is an excavation, not a liner.

Faults and shaking

The Hurricane fault runs about 87 kilometers end to end, and Special Study 127 says it is capable of earthquakes as large as magnitude 6.5 to 7. The 1992 St. George earthquake, September 2, 1992, was magnitude 5.8 per the survey's study, caused liquefaction and property damage, and triggered the Springdale landslide. The county maps faults, surface rupture hazard and a Fault Special Study Zone (layers 8 to 11) and liquefaction (16).

The plumbing consequence is on the city's own criteria sheet. The St. George Building Department publishes Seismic Design Category D, along with 105 mph wind, 21 psf ground snow and a 12-inch frost line. SDC D triggers IRC P2801.8: a water heater must be strapped with at least two straps, one in the upper third and one in the lower third of the tank, the lower strap at least four inches above the controls. That is the city's design criteria, not a plumber's habit.

Two hazards the county map doesn't show

Radon. The EPA maps Washington County as Radon Zone 2, the middle of its three categories, meaning a predicted average indoor screening level between 2 and 4 picocuries per liter. That is a prediction built from geology rather than a survey of houses, and the action level is 4. A county in the middle band still contains houses well above it. The map cannot tell you which one you own. A test can, and it costs almost nothing.

Wildfire. Layer 23 shows history, not risk. The state's Wildfire Risk Assessment Portal at wildfirerisk.utah.gov shows whether you are inside the high-risk wildland-urban interface boundary. Under Utah H.B. 48, effective January 1, 2026, cities and counties must adopt and enforce the WUI code, owners inside the boundary must create defensible space and harden their homes, and the county assesses an annual fee set by the Division of Forestry, Fire and State Lands: flat by square footage for 2026 and 2027 per the Division's program page, risk-based by triage score from 2028. The amounts are not in the statute; ask the Division.

More under plumbing

• Your backflow test notice, explained
• A pipe broke in the wall of your condo. Who pays?
• What St. George water does to a water heater