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Landmarks Big Baldy
This view of Big Baldy, the highest peak in the Little Belt Mountains is from Belt Park, south of Monarch. It shows the snow-covered peak on the skyline. The upper slopes covered by uninterrupted white snow are underlain by an igneous intrusion--the Big Baldy Laccolith. The laccolith has the shape of a sand dollar--flat bottom and rounded top. The gentle rounded shape defined by the white skyline is probably close to the top of the laccolith. The bottom of the laccolith is the treeline on the right and the bare slopes not covered with snow on the left. Beneath the laccolith are softer sedimentary rocks--shales and limestones--that erode more easily than the igneous rock above. Big Baldy is a popular destination for hikers. The only glaciers that were active in the Little Belt Mountains during the Ice Ages, carved glacial cirques on the back side of the mountain. Rhoda Lake and Twin Lakes are in these steep-walled valleys carved by glaciers. Big Baldy can be seen from Great Falls.
Neihart Baldy (and Long Mountain to the left) are an imposing sight when driving from Monarch towards Neihart. The Big Seven Mine is on the left side of Neihart Baldy, down in the trees. The distant tree-covered slopes are underlain by old Precambrian-age metamorphic rocks (mostly 1.8 billion years old, but with some rocks about 2.7 billion years old.) The upper slopes above the tree line are formed by the 1.5 billion year old Neihart Quartzite. The beds in the Neihart Quartzite are tilted away from the viewer in this photo. They come down to the highway at the Memorial Falls Trailhead (south of Neihart) where this very tough, pink rock can be seen up close. The Neihart Quartzite, which was deposited as beach sand or nearshore sand, is the lowermost formation in the Belt Supergroup and signaled the onset of the great Belt Basin. The Belt Basin formed when the Supercontinent that included North America (called Rhodinia) tried for a billion years to split apart. The split finally occurred forming a great ocean, and the part to the west of us moved far away and now forms the Siberian Platform in Russia. We are left with rocks that have quite a story to tell.
The hard sandstone layer halfway up the butte that rises above the town of Belt is the basis for the name of the butte, the name of the town, the name of the creek, the Little Belt Mountains, the Big Belt Mountains, and the Belt Supergroup, a group of sedimentary rocks that cover about a third of Western Montana, including nearly all of Glacier National Park. Most of Belt Butte is soft shale in the 95 million year old Blackleaf Formation. Apparently there was an igneous intrusion--a sill--that baked the shale under it, the shale that now forms the top of Belt Butte. Because this baked shale is harder and more resistant to erosion, the butte stands out as a topographic "high". On the northeast flank of Belt Butte is the largest collapse feature in Montana--a cave 3/4 mile long and half a mile wide where the ceiling and overlying beds dropped 600 feet. Barker Mountain
The Little Belt Mountains have the structure of a gigantic fold about 80 miles long and 30 miles wide. The fold formed when the mountains were uplifted about 55 million years ago. However, the peaks that one sees on the skyline are formed by igneous intrusions that are about 50 million years old. Barker Mountain is the dominant feature in the Little Belts when traveling from Great Falls. It is a circular intrusion called a laccolith. The magma squirted between a couple of beds and had enough pressure to lift the overlying layers. This resulted in a sand-dollar shape for the intrusion--flat bottom and rounded top. Big Baldy on the far horizon is the highest peak in the Little Belt Mountains. Thunder Mountain
This photo was taken from the same spot as the Barker Mountain photo above, but looking more to the right. Both Thunder Mountain and Tiger Butte are laccoliths. The Thunder Mountain Laccolith has a gentle rounded shape as indicated by the skyline. Tiger Butte is more sharply updomed (see next photo). Tiger Butte
Tiger Butte was named for its stripes. The "stripes" are beds of Madison Limestone. Inside Tiger Butte is a core of igneous rock. So much molten magma intruded between the sedimentary layers that the resulting shape resembles a World War I steel helmet. On the right side of the butte the beds are tilted to the right. Beyond the ranch house the beds are tilted towards the viewer. On the back side of Tiger Butte the beds are tilted away from the viewer. Some of the igneous rock responsible for this "big bulge" in the sedimentary rocks can be seen along the road that goes up the coulee on the right side of the butte. Sluice Boxes
Belt Creek cut a vertical walled "slot" through the Madison Limestone. This stretch of Belt Creek is known as the "sluice boxes" after the device used to recover gold in placer operations. The creek does not contain gold, but it is now a "gem" of a state park. The Man Face
Watch out! When you are driving northbound on U.S. 89 at Mile 46, the great stone face is "watching you". This cliff is nearly 300 feet high. It is made of 370 million year old Jefferson Dolomite. The Old Turk
Standing guard in Monarch Canyon at Mile 51.8. This pillar is made of limestone. Going up Monarch Canyon one travels up through the entire 1700 foot thickness of Madison Limestone. Notice the many caves in the limestone as you go up the road. The limestone is formed from shells of small animals that lived on the surface of the sea when this area was on the equator 330 million years ago. Some beds contain abundant fossils of larger animals--crinoids, brachiopods, bryozoa, and horn corals. When the limestone is uplifted so that it is above sea level, ground water slowly percolates through the cracks, dissolves the limestone, and forms caves. Other Landmarks The Ship Limestone Arch Ice Caves
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