We would be collecting today from the Morrison formation, deposited roughly 150 million years ago. The Ottinger guide indicates a dozen good fossil and mineral collectibles in this strata, recognized by its distinctive red and green shales.
Huge domes of green weathered stone loomed before us as we pulled over on a gentle rise. We walked a short way off the road, toward Arches National Monument, visible on the skyline. But who had time to look at the skyline when the ground was absolutely littered with glassy multicoloured chalcedony of exceptional consistency?
Truly beautiful cabbing material, the translucent luster of this find is hard to picture from a photograph. An unearthly glow sheens from vibrant earth tones. Finding them was easy, as the thin surface dirt was blown and washed away around the tops of these, nature’s floor tiles. It’s the carrying that presented the challenge. Bring a big bag.
Mixed in with all the chalcedony were occasional pieces of petrified wood and some fragments of dinosaur bone. The wood was unremarkable, a listless slate gray in color without dramatic grain, and no pieces of significant size, at least at this spot. I guess it’s true; I’m getting jaded, dismissing any find of petrified wood so cavalierly. The dinosaur bone fragments could easily be overlooked by an untrained eye as just more rocks, or possibly agates or chalcedony.
To an experienced eye, though, the subtle textures, coloration, and grain of certain rocks is indicative of fossilized bone, and the particular weathering patterns of this extremely tough quartz material is also an indicator.
The occasional dino bone shard presents a special situation. Although casual collecting without use of mechanized gear is allowed on public lands such as this, no vertebrate fossils may be legally collected on public lands anymore, under highly restrictive laws enacted in 1976.