The Arizona Geological Survey has a 45-page booklet discussing some geologic hazards that home buyers should be aware of. You can download the booklet here. Subjects include floods, earthquakes, problem soils, mass movement, subsidence & fissures, radon, karst (caves), abandoned mines, and volcanic hazards.

“Our purpose is not to say that any particular parcel of land should not be developed. Rather, in those areas where geologic hazards or limitations are known to be present or where they may potentially exist, knowledge of their existence should help guide planning, design, construction, and maintenance. It remains up to property buyers or owners and local government to determine the level of acceptable risk from geologic hazards.”

In the desert, ironically, flooding is the most widespread, common, and damaging of all the geological hazards. This section explains floodplains and “100-year floods” and notes the areas most prone to this hazard.

“Over the past 150 years, more than 20 earthquakes having magnitudes greater than 5 have occurred in or near Arizona, and all of Arizona has experienced at least moderate earthquake shaking. The magnitude 7.4 Sonoran earthquake of 1887, which was centered about 40 miles southeast of Douglas, caused 51 deaths in Sonora and extensive property damage throughout southeastern Arizona. The Yuma area has experienced repeated damage from earthquakes that occurred in southern California or northern Mexico.” This section of the booklet shows maps which rate potential hazards.

“Damage to structures in Arizona is commonly related to soil characteristics, with expansive (shrink/swell) soils and collapsing soils causing the most problems. Cracking of foundations, walls, driveways, swimming pools, and roads cost millions of dollars each year in repairs.” Such damage is related to the amount and type of clay in the soil.

The section on mass movement deals with landslides and debris flows which occur along mountain fronts and at the base of cliffs.

Land subsidence and earth fissures occur in areas in which groundwater is withdrawn faster than natural recharge.

“Radon gas is a radioactive element that is produced by the decay of uranium, which is present in virtually all rocks and soils, typically at concentrations of 1-4 parts per million.” The hazard is that radon can seep into buildings through cracks in the foundation. A sufficient concentration poses a health hazard. This section explains the danger and shows the areas of Arizona especially prone to radon emissions.

Karst terrain is developed in areas underlain by limestone, especially on the Colorado Plateau. Sinkholes may develop as cave systems mature.

 Old mine workings present a danger of toxic substances as well as falling in them.

Volcanic activity has occurred frequently in Arizona, some just 800 years ago (see ). The San Francisco volcanic field near Flagstaff is considered active. “Hazards associated with volcanic activity include ash and cinders that can overload the weight-bearing capacity of some roofs. Houses built in the Flagstaff area, where snow is routine, are already designed with loading in mind. Volcanic gases include carbon dioxide and sulfur gases that are sometimes at concentrations that may be harmful to breath.”

The AZGS booklet is well-illustrated with maps and other graphics showing the general locations of each hazard and what to expect.