North of I84, north of the Simco Road Exit 74, out on the Mayfield loop of caches, in the area of the Main Oregon Trail Back Country Byway, there are a number of interesting and fun rock formation scattered around. Take them in and see the sights as you are caching your way down the historic trail.
MAIN OREGON TRAIL BACK COUNTRY BYWAY:
Starting at the crossing of the Snake River, the Oregon Trail Back Country Byway follows the route of the pioneers as they crossed the Idaho desert. (This portion of the trail is between Mountian Home and Boise, just north of Exit 74). Take a journey back in time as you walk in the ruts created by thousands of emigrants in search of a new home. Much of this route appears the same today as it did when pioneers traveled this route.
SOURCE: https://visitidaho.org/things-to-do/scenic-byways-backcountry-drives/main-oregon-trail-backcountry-byway/
Volcanic Rock Types:
Rocks are not all the same. Some are heavy, some are light. Others are dark, while some can be almost pure white. Even igneous rocks that are all formed from magma in the Earth’s mantle can look very different.
Volcanic rock is an igneous rock of volcanic origin. Volcanic rocks are usually fine-grained or aphanitic to glassy in texture. They often contain clasts of other rocks and phenocrysts. Phenocrysts are crystals that are larger than the matrix and are identifiable with the unaided eye. They were created during fractional crystallization of magma before extrusion. Volcanic rocks are named according to their chemical composition. Basalt is a very common volcanic rock with low silica content. Rhyolite is a volcanic rock with high silica content. Rhyolite has the same chemical composition as granite and basalt is compositionally equal to gabbro. Intermediate volcanic rocks include andesite, dacite, and latite. Volcanic rocks often have a vesicular texture, which is the result voids left by volatiles escaping from the molten lava. Pumice is a rock, which is an example of explosive volcanic eruption. It is so vesicular that it floats in water. Pyroclastic rocks are the product of explosive volcanism. They are usually felsic (high in silica). Examples of pyroclastic rocks are tuff and ignimbrite. Shallow intrusions, which possess structure similar to volcanic rather than plutonic rocks are also considered to be volcanic.
What are igneous rocks? Igneous rocks are formed from the solidification of molten rock material. There are two basic types: 1) intrusive igneous rocks such as diorite, gabbro, granite and pegmatite that solidify below Earth's surface; and 2) extrusive igneous rocks such as andesite, basalt, obsidian, pumice, rhyolite and scoria that solidify on or above Earth's surface.
ROCK TYPES:
Andesite is a fine-grained, extrusive igneous rock composed mainly of plagioclase with other minerals such as hornblende, pyroxene and biotite.
Basalt is a fine-grained, dark-colored extrusive igneous rock composed mainly of plagioclase and pyroxene.
Diorite is a coarse-grained, intrusive igneous rock that contains a mixture of feldspar, pyroxene, hornblende and sometimes quartz
Gabbro is a coarse-grained, dark colored, intrusive igneous rock that contains feldspar, augite and sometimes olivine.
Granite is a coarse-grained, light colored, intrusive igneous rock that contains mainly quartz and feldspar minerals.
Obsidian is a dark-colored volcanic glass that forms from the very rapid cooling of molten rock material. It cools so rapidly that crystals do not form.
Rhyolite is a light-colored, fine-grained, extrusive igneous rock that typically contains quartz and feldspar minerals.
Scoria is a dark-colored, vesicular, extrusive igneous rock. The vesicles are a result of trapped gas within the melt at the time of solidification. It often forms as a frothy crust on the top of a lava flow or as material ejected from a volcanic vent and solidifying while airborne.
The Cache:
This cache is located off the Main Oregon Trail road, and the formation you are looking for is just North West of the corrdinate. The formation is easy to spot and see clearly from the road, there is no need to cross fenses to see it and to get the answers for this cache. Looking at this rock formation, it stands out as unique amongst the others leading up to this area no matter which way you approach. It has an interesting shape and form. Understanding volcanic activity and knowing the the eruptie force of the explosion brings minerals from deep within the earth, and the consequent flow leaves deposites. Looking across the plains here and seeing the large and numerous rock formations you can see how volcanic activity has shaped the area.
To log this cache:
1. Looking at the rock formation North West of GZ, as well as the other large rocks in the area and the other formations lining the hills, you will see darker rocks, some rather large. These are volcanic rocks. Based on the descriptions provided, and possible volcanic knowledge, what kind of volcanic rocks are these?
2. At the cache sight there is a natural rock formantion that I found very intriging and beautiful. You will see this natural formation as you look North West. Describe the formation.
BONUS - OPTIONAL. about .1 miles East of this location is an Oregon Trail Information Marker and another rock formation along the road. How was this rock formation used by Oregon Trail Travelers?
Please do not post you answers for this cache in your log. Email me, tell me the number in your party and who they are, one email per party should be fine. Have fun, thanks.