Private Well WaterA field guide to the water under your house
Aquifers of the United States

What's under the country

An aquifer is rock or sediment that holds water in its pores and cracks — not an underground lake. What the rock is made of decides how much water a well gets, how fast pollution reaches it, and what the water picks up along the way.

USGS principal aquifers by rock type63 mapped · 26 with a page here
Ada-Vamoosa aquifer — SandstoneArbuckle-Simpson aquifer — Limestone & dolomiteBasin and Range basin-fill aquifers — Sand & gravelBasin and Range carbonate-rock aquifers — Limestone & dolomiteBiscayne aquifer — Limestone & dolomiteBlaine aquifer — Limestone & dolomiteCalifornia Coastal Basin aquifers — Sand & gravelCambrian-Ordovician aquifer system — SandstoneCastle Hayne aquifer — Limestone & dolomiteCentral Oklahoma aquifer — SandstoneCentral Valley aquifer system — Sand & gravelCoastal lowlands aquifer system — Semiconsolidated sandColorado Plateaus aquifers — SandstoneColumbia Plateau basaltic-rock aquifers — Crystalline & volcanicColumbia Plateau basin-fill aquifers — Sand & gravelDenver Basin aquifer system — SandstoneEarly Mesozoic basin aquifers — SandstoneEdwards-Trinity aquifer system — Sandstone & carbonateFloridan aquifer system — Limestone & dolomiteHawaiian Sedimentary deposit aquifers — Crystalline & volcanicHawaiian Volcanic-rock aquifers — Crystalline & volcanicHigh Plains aquifer — Sand & gravelJacobsville aquifer — SandstoneKingshill aquifer — Limestone & dolomiteLower Cretaceous aquifers — SandstoneLower Tertiary aquifers — SandstoneMarshall aquifer — SandstoneMississippi River Valley alluvial aquifer — Sand & gravelMississippi embayment aquifer system — Semiconsolidated sandMississippian aquifers — Sandstone & carbonateNew York and New England carbonate-rock aquifers — Limestone & dolomiteNew York sandstone aquifers — SandstoneNorthern Atlantic Coastal Plain aquifer system — Semiconsolidated sandNorthern Rocky Mountains Intermontane Basins aquifer system — Sand & gravelOrdovician aquifers — Limestone & dolomiteOzark Plateaus aquifer system — Limestone & dolomitePacific Northwest basaltic-rock aquifers — Crystalline & volcanicPacific Northwest basin-fill aquifers — Sand & gravelPaleozoic aquifers — Sandstone & carbonatePecos River Basin alluvial aquifer — Sand & gravelPennsylvanian aquifers — SandstonePiedmont and Blue Ridge carbonate-rock aquifers — Limestone & dolomitePiedmont and Blue Ridge crystalline-rock aquifers — Crystalline & volcanicPuerto Rico North Coast Limestone aquifer system — Limestone & dolomitePuerto Rico south coast aquifer — Sand & gravelPuget Sound aquifer system — Sand & gravelRio Grande aquifer system — Sand & gravelRoswell Basin aquifer system — Limestone & dolomiteRush Springs aquifer — SandstoneSeymour aquifer — Sand & gravelSilurian-Devonian aquifers — Limestone & dolomiteSnake River Plain basaltic-rock aquifers — Crystalline & volcanicSnake River Plain basin-fill aquifers — Sand & gravelSoutheastern Coastal Plain aquifer system — Semiconsolidated sandSouthern Nevada volcanic-rock aquifers — Crystalline & volcanicSurficial aquifer system — Sand & gravelTexas coastal uplands aquifer system — Semiconsolidated sandUpper Cretaceous aquifers — SandstoneUpper Tertiary aquifers — SandstoneUpper carbonate aquifer — Limestone & dolomiteValley and Ridge aquifers — Sandstone & carbonateValley and Ridge carbonate-rock aquifers — Sandstone & carbonateWillamette Lowland basin-fill aquifers — Sand & gravelHawaiiPuerto Rico (2×)
  • Sand & gravel
  • Semiconsolidated sand
  • Sandstone
  • Limestone & dolomite
  • Sandstone & carbonate
  • Crystalline & volcanic
Outlines: USGS Principal Aquifers of the 48 conterminous states, Hawaii, Puerto Rico and the U.S. Virgin Islands. Where aquifers are stacked, the map shows the shallowest. Tap an aquifer to open its page.

Unconsolidated sand and gravel

Water fills the spaces between loose grains of sand and gravel, usually close to the surface.

Semiconsolidated sand

Sand layers, partly cemented, stacked between clay beds that slow water moving between them.

Sandstone

Sand grains cemented into rock; water moves through the pore space that is left and through cracks.

Carbonate rock

Limestone and dolomite that water slowly dissolves, opening cracks into channels and caves.

Sandstone and carbonate rock

Layers of sandstone and limestone stacked together; water moves through pores in one and channels in the other.

Igneous and metamorphic rock

Granite, gneiss, schist or lava rock: almost no pore space, so water lives only in fractures (or between lava flows).