The Alberton Gorge of the Clark Fork River offers the best whitewater rafting in Western Montana. In early spring, the Alberton Gorge is a big water raft trip. The Clark Fork River is the largest river by volume in Montana and it feels like it every spring. As the water drops, the gorge becomes more defined and forms dozens of Class III rapids with names like Triple Bridges, Ice Box, Roller Coaster, Boat Eater, Tumbleweed, Fang and Davey Jones’s Locker. The calm stretches between the rapids make this the perfect family rafting trip allowing for swimming and water fights. The gorge is lined with spectacular canyon walls, raptors, wildlife, and incredible rapids.
Our headquarters, Crystal Springs, overlooks the Alberton Gorge and is only a few minutes from both the put-in and take-out making last minute changes and logistics easy. After your river adventure, kick back, relax and enjoy a cold beverage or picnic on one of our decks overlooking the Alberton Gorge.
Alberton Gorge Geology
During the last ice age, approximately 20,000 years ago, the Clark Fork Valley rested along the southern edge of the Cordilleran ice sheet covering western North America. The ice sheet advanced and formed an ice dam on the river, creating Glacial Lake Missoula, which stretched through the Clark Fork Valley across central Montana. The periodic rupturing and rebuilding of the ice dam released the Missoula Floods, a series of catastrophic floods down the Clark Fork and Pend Oreille Rivers into the Columbia, which sculptured many of the geographic features and rapids you see on the Alberton Gorge today.
The Belt Supergroup (Belt rock) is a collection of mostly fine-grained sedimentary rocks found in the Alberton Gorge. Sedimentary rocks form by deposition of fine grained material on the floor of bodies of water.
The sedimentary rocks that form the Belt Supergroup were formed in the Precambrian (Mesoproterozoic) age (1 billion to 1.6 billion years ago – WOW…..that’s almost half the age of the Earth!). The Mesoproterozoic was the first period of Earth’s history in which a good geological record still survives. The continents we have on earth today existed prior to the Mesoproterozoic, but relatively little is known about them.
The original appearance of the Belt rocks when they were deposited over a billion years ago resembled a mud flat, and the original material was clay, silt, and fine sand. These muddy-silty deposits were buried and experienced weak metamorphosis (a fancy word for saying they have been changed or transformed by being buried and put under heat and pressure).
The current theory is that an inland sea (slightly similar to a small Mediterranean Sea) existed in the North American Craton (Craton – the ancient geological core of the North American continent), and the deposits in this sea form the Belt Rocks.
Some cool features (geologically speaking) of the Belt rocks in the Alberton Gorge:
- Ripple marks (from waves in shallow water) exist in the formation. This is rare because of the great age of the Belt rocks (usually these structures are destroyed by metamorphosis or other geologic processes).
- They contain no obvious, visible fossils of plants or animals. There is evidence of extremely primitive plants and bacteria, the rocks offer no trace of animal life. This is thought to be because very little life existed on Earth at this time except for life in the ocean….and the inland sea that formed these rocks was not connected to the ocean.
- Mudcracks are abundant between layers of Belt rocks; These were caused by surfaces that dried in the sun before being flooded by water that brought more mud or silt, which preserved the delicate features.
Many of the layers of mudstone in the Belt Supergroup are colored interesting shades of green or reddish purple. The red, purple, and maroon color is due to the red mineral called “hematite” formed as iron reacts with oxygen from the atmosphere. It is believed that the green rocks were formed in deeper water where oxygen was less available. The alternating green and red layers suggest fluctuations in the depth of the Belt Inland Sea.
Give us a call and get ready for an adventure!