Trapped gasses formed cavities within the rhyolite, and millions of years of ground-water circulation allowed minerals to precipitate into the cavities. The result is geodes with spherical shapes and crystal-lined cavities. Roughly 32,000 to 14,000 thousand years ago, a large body of water known as Lake Bonneville covered most of western Utah. The lake's wave activity eroded the geode-bearing rhyolite and redeposited the geodes several miles away in the Dugway geode bed area as lake sediments.
Most geodes are typically hollow whereas others are completely filled with massive, banded quartz.
Recently, people have bypassed the turnoff because the sign to the geode bed area was missing. The easiest technique is to find an area of past excavations and start digging to locate the proper horizon where the geodes can be found. Examine all stones that are encountered. The geodes are fairly easy to recognize due to their spherical shape and light weight. Most geodes are 2 to 3 inches in diameter and are typically lined with small quartz crystals that give the cavity a sugary appearance.