Prickly Pear Canyon Earthcache EarthCache
Prickly Pear Canyon Earthcache
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Difficulty:
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A roadside earthcache at a designated parking area.
A Brief History: Although this multi-hued and rugged canyon was well-known to Native Americans for thousands of years, it was first recorded by road-builder John Mullan in 1859. He called this rocky canyon “a perfect defile” and “by far the most difficult of any point along the [road], from Hell’s Gate to Fort Benton.” In 1865, the Territorial Legislature granted a license to the Little Prickly Pear Wagon Road Company to build a toll road through the canyon. A year later, in 1866, Helena merchants James King and Warren Gillette bought the road and spent $40,000 upgrading it. By then traffic on it between Fort Benton and Helena had become so heavy, that the men were able to recoup their expenditure within two years. By the early 1870s, it was part of the Benton Road, an important freight and passenger route in the territory. Thereafter, other roads and a railroad were constructed through the Prickly Pear Canyon, culminating in the completion of Interstate 15 in 1967. Montana’s first Interstate rest area, here at Lyons’ Creek, was built in 1965.
Here nestled deep in the Big Belt Mountains, is one of the most spectacular canyons in Montana. More than a billion years ago an ancient inland seaway deposited these shales and sands, which over time, became these vibrant red and green mudstones called “Spokane Shale” for the Spokane Hills east of Helena. The Big Belts themselves consist primarily of Spokane Shale. They contrast with the magnificent white cliffs of Madison Limestone exposed in the nearby Gates of the Mountains and the drab gravels of Confederate Gulch to the southeast. The greenish colors in the mudstones are provided by tiny amounts of iron minerals that formed on mudflats that were low in oxygen; the intervening pinkish layers oxidized in contact with slightly greater amounts of oxygen.
To claim this find, email the cache owner the answers to the following questions. Please note "PP Canyon Earthcache" in the top line of your email. You will not hear from the cache owner unless clarification of answers are needed. Go ahead and log it after sending your email.
1. In what "era" did the shales and sands that make up this rocks get deposited?
2. How long ago were these rocks crumpled, folded and faulted to form the Rocky Mountains?
3. Look around at the "folded" rocks. The most pronounced crumpling occurs nears the eastern edge of the rockies in what "belt"?
Optional Geo Activity!
For the next five miles count how many times you can see the red and green stone, called Spokane Shale, in the canyon formations.
Additional Hints
(No hints available.)