St. Peter's Dome is located in the western end of the Penokee Range and is a red granite formation that rises to an elevation of 1,565 feet. The range was formed 1.8 billion years ago. A period of igneous intrusions about 1.1 billion years ago formed the granite dome.
There is a $5 parking fee at the trailhead. The hike to St. Peter's Dome is 4 miles round trip. The trail has moderately steep climbs. To reach St. Peter's Dome (locally known as Old Baldy) hike east to the 1930s Civilian Conservation Camp (CCC), old stone fireplaces, an artesian well and a round cistern are all that remain of the campground, and continue east up the gradually climbing trail. The trail to the dome becomes narrower as you walk across much steeper slopes. There is a lake sized beaver pond on your left. As you continue east, the trail drops in elevation and crosses a rocky stream bed. Beyond the stream the trail becomes steeper and rockier. After a short distance the grade becomes gentler; you cross a snowmobile trail. At the base of the granite outcrop you will find a jumble of large broken rock from a quarry. The trail follows the old road for a hundred feet and then turns left off the road and begins to climb. After two switch backs, the trail reaches a grassy opening. Continue on the trail and climb to the overlook and shear drop on the north face of St. Peter's Dome. On a clear day, you can see Chequamegon Bay of Lake Superior and the Apostle Islands.
What Type of Rock Is It?
Igneous Rock is formed when magma cools underground and crystallizes or when it erupts unto the surface of the ground, cools and crystallizes. Magma that erupts onto the surface is called lava. When magma cools slowly underground the crystals are large enough to see. When it cools quickly on the surface, the crystals are very small and you would need a magnifier or a microscope to see them. Sometimes, when the magma cools very quickly, it forms a kind of black glass that you cannot see through.
What Minerals Make Up the Rock?
Quartz, feldspars (microcline, orthoclase, albite), biotite, muscovite; Sometimes contain: hornblende, augite, magnetite, zircon
What Does It Look Like?
The feldspars give granite most of its color, which may be white to light gray, yellowish, or pink. The quartz is usually smoky gray or white. Black specks of biotite, or sometimes hornblende, are common. So is silvery to brownish muscovite. Granite is coarse grained to very coarse grained. The crystals are randomly arranged (unlike gneiss where they are in lines or layers).
How Was It Formed?
Granite forms deep in the earth's crust from cooling magma. The magma contains a lot of silica (quartz). Slow cooling produces the large crystals in granite.
Color/Texture Classification Key
TO LOG THIS CACHE:
1) Classify the rock you’re standing on using the Color/Texture Classification Key.
2) What’s the percentage of the different “colors” in this rock?
3) Take a picture of you and the view!
To log this cache -mail me HERE.
- Parking (USFS) $5 - N46 20.989 W90 55.372
- Trail to Morgan Falls - N46 20.983 W90 54.941
- Bench - N46 21.079 W90 54.213
- Benchmark - N46 21.093 W90 53.836