Extending across southwestern Idaho between the Owyhee Mountains and the Boise Front is the broad valley of the western Snake River Plain, which evidence indicates began as a continental rift. The earth's crust began to be pulled apart, northeast to southwest, stretched thin like taffy, and the Owyhee Mountains and the Boise Front rose along faults bordering the rift, reaching their present heights during the Neogene Period.
Geologists think water from melting glaciers caused Lake Idaho to overflow to the west in a massive flood that gouged Hell's Canyon, along the present-day Idaho-Oregon border.
Sediments left behind became the Chalk Hills and Glenns Ferry Formations. They form the deep sandy slopes and ridges that plants like Mulford's milkvetch need to grow and which are found in only in three areas of Idaho: the Owyhee Front, the Boise Foothills and the area around Weiser, ID.
The tiny round pieces of limestone found on the Flat are called ooids, known as oolite ("egg stone") when deposited in larger formations. The oolite on the Mud Flat, known as the Shoofly Oolite, is part of the Glenns Ferry Formation and one of the world's largest freshwater oolites.
Ooids form when calcium carbonate precipitates around individual grains of sand.
Wave action in Lake Idaho that varied with the seasons, the weather and the type of sediment in the water at the time washed the ooids back and forth in the shallows, depositing them in thicknesses of 2 to 40 feet on the steeper benches near the shores. The Shoofly Oolite is unique because it formed in fresh water. Sea water is more likely to have the necessary wave action, and saltier lakes the proper chemistry.
Beach sands of varying thickness underlie the oolite. Siltstone forms the stratum immediately above it.
After Lake Idaho drained, erosion carried away softer sediments but left the more resistant oolite to weather above the mud flats. Small deposits are exposed here and there across the 40 miles that separate the flats and the town of Murphy. In some places, the exposed oolite has been sculpted into hummocks, small arches or other intriguing shapes, forming a natural sculpture garden.
The five acre enclosure secures the oolite formations and small hills. Hiking is allowed in side the fenced area. Visitors may park in the parking area near the coordinates. If health does not permit you will be able to see many formations and inspect shoofly oolite from the parking area.
Logging requirements:
Send us an email with answers to these questions:
Standing at the coords look west:
1. How thick is the banding and how high do you estimate it to be?
2. How many cliffs do you see?
3. Now look east at the sign. What does it say?
It is not required but if you would like to post a picture of the area or yourself at the location feel free.
Please Note:
1. You must answer all the questions in your email to us.
2. Your logging this cache and sending us the email should happen at around the same time.
3. Begin your email with the name and geocaching code of this Earthcache, your name(s), and the number of people in your group.
4. We won't respond unless you send incorrect answers.
We from the League wish you all the best. Have a safe adventure!