Oolite? What the heck is that? It’s not a new beer or some kind of new fad diet food. Read on to find out.
The BLM has a “new” interpretive site south of Grand View on Mud Flat Road. This geologic information site is pretty cool and there is a walking trail on site also.
While hiking and enjoying the great Idaho outdoors, sometimes it’s nice to actually understand the area to gain a better appreciation of what I’m seeing.
1. The Big Picture
What it says:
- Extending across southwest Idaho between the Owyhee Mountains and Boise Front is the broad valley of the western Snake River Plain. Evidence indicates that the Plain began as a continental rift about 12 million years ago. Here, the earth’s crust was pulled apart, northeast to southwest, and was stretched thin like taffy.
- As crustal extension progressed between 11 and 9 million years ago, the Owyhee Mountains and the Boise Front responded by rising to their present height along faults bordering the rift. Now a valley, the Plain became a basin for Lake Idaho. Some 200 miles long and 35 miles wide, Lake Idaho drained south into Nevada.
- Thousands of feet of sediment were deposited on the Lake’s bottom over its 6.5 million years of existence, interrupted at times with layers of basalt and volcanic ash (tuff) from eruptions of adjacent volcanoes.
- Geologist think that 2 to 4 million years ago, water from melting glaciers caused Lake Idaho to overflow to the west.. Captured by the Snake River, the waters drained out in a massive flood that gouged Hell’s Canyon. The sediments left behind from Lake Idaho are known as the Chalk Hills and Glenns Ferry Formation.
2. Shoofly Oolite
What it says:
- The natural sculpture garden is a section of the Glenns Ferry Formation called the Shoofly Oolite. Oolite is sedimentary limestone composed of tiny ooids, which form when calcium carbonate precipitates in concentric layers around individual grains of sand. The Shoofly Oolite is one of the largest freshwater lakebed oolites known in the world.
- Most other examples of ooid formation and deposition are found in wave-agitated sea waters or on the beds of much saltier lakes. 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.
- Erosion carried away softer siltstone and volcanic tuffs but left the more resistant oolite to weather above the mudflats. Small, isolated deposits are exposed discontinuously across the 40 miles between this spot and Murphy. In some places, the upper surface of the oolite has been sculpted into hummocks, small arches, and intriguing shapes.
- Beach sands of varying thickness underlie the oolite. Siltstone, deposited by lake waters, forms the stratum above it. Rivers and fans at the base of the adjacent mountain slopes later deposited a veneer of alluvium over the lake deposits.
- The physical and chemical properties of the Shoofly Oolite provide the foundation for the unique set of plants and fossils found here. Few other lands in Idaho support such a rich suite of rare species in such a small area.
3. Vegetation of the Shoofly Oolite
The 5 Rare Plants in the Shoofly Oolite Formation
- Mulford’s Vilkvetch (Astragalus mulfordiae)
- Snake River Milkvetch (Astragalus purshii var. ophiogenes)
- Packard’s Cowpie Buckwheat (Eriogonum shockleyi var. packardiae)
- White-margined Wax Plant (Glyptopleura marginata)
- White Eatonella (Eatonella nivea)
While the information on the sign indicated these plants are rare, in my experience only the White Eatonella seems to be the only “rare plant” in the Owyhee’s. Your mileage may vary.
Coordinates for the BLM Oolite Interpretive Site on Mud Flat Road: 42.837189, -116.122149
Thanks,
