GRAND VIEW — It takes an hour by car through the desert east of Boise and another half-mile on foot through a sea of sagebrush before you start to see signs of Lake Idaho.
The lake itself, which once covered the Treasure Valley, dried up millions of years ago. The fossils, rare soils and almost alien rock formations it left behind remain a draw for hikers at the Shoofly Oolite Interpretive Trail in Owyhee County.Fall is the perfect time for this short desert hike, which starts off of Mud Flat Road a few miles south of Grand View. The cooler temperatures in November mean you won’t overheat on the unshaded trail and rocks. (Plus, you’re less likely to see snakes.)
Hiking to Idaho’s oolite
We made it to the trailhead on a windless Saturday afternoon. Unless you’re a fan of flying dust and sand, keep an eye on the forecast. It’s about an hour from Boise via Simco Road, and the entire route is paved. There’s a small gravel turnout that serves as a parking area and trailhead. There’s not much space for multiple vehicles, but we saw only one other group during our visit.
The trail crosses about half a mile of land managed by the Bureau of Land Management. At the trailhead, which is marked by a wooden barrier, the BLM has installed signs explaining the significance of the oolite.
“Oolite (egg stone) is sedimentary limestone composed of tiny ooids, which form when calcium carbonate precipitates in concentric layers around individual grains of sand,” one sign reads. “... Wave action that varied with the seasons, the weather, and the types of sediment in the water washed the ooids back and forth in the shallows on the southwestern side of Lake Idaho, depositing them from 2 to 40 feet thick on steeper benches near the shore.”
The Shoofly Oolite — named for nearby Shoofly Creek — is one of the largest ooid formations in the world, according to the BLM. The formations line the rim of a small plateau about a half-mile from the trailhead.
The trail is short, well-marked and in great shape. It takes about 15 minutes to get to the edge of the rim where the rock formations are visible. From here, the trail becomes harder to follow as the soft soil of the oolite creates sandy hills similar to those at the nearby Bruneau Sand Dunes.
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There are a few already-worn paths to choose from, some a bit steeper than others, that take you up the short climb to the top of the plateau where the trail ends.
That’s where the real adventure begins.
Explore oolite arches and craters
Once you reach the plateau, you can easily explore the nooks and crannies created in the Pliocene Epoch by the ancient Lake Idaho.
You can sit in the round craters hollowed out of heaped oolite domes or climb along rolling expanses of craggy rock. Parts of the rock form a window that frame the Owyhees to the west, while others create overhead arches reminiscent of the iconic red sandstone structures at Zion and Arches national parks in Utah.
Watch your step — the sand and ooids can create a slipping hazard on the rocks.
Even the landscape surrounding the oolite structures is fascinating. Some stretches of the flats have dried into cracked mud dotted with flat stones and rare plants, like Mulford’s milkvetch. BLM officials urge visitors to be mindful of those plants and also to avoid the sandy edges of the plateau, which are susceptible to erosion.
Occasionally, visitors find fossils left over from Lake Idaho — most often freshwater mollusks (like snails) but small fish fossils also have been found there. BLM spokeswoman Lindsey Neiwert said it’s illegal to remove vertebrate fossils for personal use, but visitors are allowed to take mollusk or plant fossils, though it’s not encouraged. It’s also legal to take small quantities of petrified wood from the site. The oolite rock structures can be found in scattered clusters along what’s called the Glenns Ferry Formation, so intrepid explorers can follow the edge of the plateau to see even more of the odd rocks.
To return to the parking area, circle back to where you climbed the plateau and follow the same trail back.