Guides

• How SinkholeOdds rates a county — The USGS map, the grid sample and the thresholds behind every SinkholeOdds county tier, with their limits stated.
• Why "buried" limestone is not automatically safe — 351 counties have their soluble rock mostly under thin cover. That is where cover-collapse sinkholes, the sudden kind, form.
• Gypsum and salt: the rock that dissolves fastest — 271 counties sit partly on evaporite rock. Why a small share of gypsum or salt can matter more than a large share of limestone.
• Florida sinkhole insurance: what a standard policy covers — Florida law splits catastrophic ground cover collapse from sinkhole loss. 61 of 67 Florida counties land in the top two tiers.
• Signs of a sinkhole under a house, and how inspection works — The warning signs inspectors look for, what a sinkhole investigation actually does, and when a county rating means you should order one.
• No limestone, but still holes: pseudokarst explained — 108 counties have no soluble rock mapped but do have pseudokarst: soil piping or lava tubes that can open voids too.