Outcrop shows you the geologic map of wherever you are standing, and can lay it over the land through your camera.

Open it and the sheet at the bottom names the rock under you, how old it is, and the region you are in. Pull it up for that rock's page: what it is made of, where it falls in Earth's history, the rock column for the area, and fossils found in it nearby. Tap anywhere on the map to read that spot instead.

WHERE IT FORMED
A unit's page shows where its spot lay when it formed, on C. R. Scotese's map of the Earth at that age, and turns the map into a globe there. Press play to watch it ride its plate to where it lies today, through every map between.

LIVE
Hold your phone up to the view and Live drapes the geologic map over the hills in front of you, on a 3D model of the terrain. The circle in the middle names the rock it rests on. Peaks, passes and lakes are labelled, so you can tell which ridge is which. If the compass is a little off, drag to line it up. From the passenger seat, it follows the land as you go. Take a picture of the view, the map drawn on it and the rock under the circle named, to save or share.

THREE MAPS
Bedrock: Macrostrat's geologic map, stitched together from published maps at many scales around the world.
Quaternary: the young deposits on top, like glacial till, river gravel and dunes, with the young faults, across the United States.
Soils: the USDA soil survey, across the United States.

SAVED AREAS
No signal at the trailhead? Outline an area of up to 2,500 km² before you go, and Outcrop keeps the maps, the terrain, satellite imagery if you want it, and Live's labels on your phone. It tells you how big the save will be first.

DETAILS
• Free, with no account and no ads
• Works offline in your Saved Areas

Geologic maps from Macrostrat and the USGS. Soils from USDA NRCS. Fossils from the Paleobiology Database. Ancient maps and plate motions from C. R. Scotese's PALEOMAP project. Elevation from Mapterhorn. Place names © OpenStreetMap contributors. Basemap and imagery from Mapbox.

Also check out our other app, Flyover Country, which tells you about the view out of the airplane window seat!