The out-and-back Crater Spur Trail leaves from the western side of the Syncline Loop Trail
and travels eastwards into the actual crater of the Upheaval Dome. Follow cairns through a dry wash, leaving it only occasionally to get around large outcrops or drop offs. The trail ends at a signpost. From here you can go off trail to poke around in earth that was once 1000 feet underground. You can also get up close to the jumbled pile of rock that was pushed up in the center of the crater (called a rebound peak).
Geologists are not sure, but most think the Upheaval Dome was caused by a meteorite 500-1000 feet across hitting the earth, causing a crater and then erosion slowly reshaping the land. Another theory is that a thick layer of salt deposited by ancient seas was pushed up through layers of rock creating a salt bubble that eroded away over time. The presence of shocked quartz has led most to believe the meteorite explanation.