ice and calcite crystals. The ice caves used to be open to the 

 public, but their present status is unknown. Mystery Cave, which 

 has been locked to prevent vandalism, is reported to contain a 

 variety of stalactites, flowstone, and soda straws. 



Bighorn Canyon is a classic example of a superimposed 

 drainage, and while still impressive, must have been spectacular 

 prior to being flooded when Yellowtail Dam was built. The river 

 has lowered itself into a canyon that is roughly 600 feet deep. 

 The canyon is now designated a National Recreation Area. 



Northwest of Billings is an interesting area that is drained 

 internally. The broad area is known as the Lake Basin which also 

 encompasses the smaller Commache Basin. Water from these basins 

 does not contribute to the flow of either the Yellowstone or 

 Missouri rivers. Within the basin, one can find many ephemeral 

 lakes, which may have been formed as prevailing winds from the 

 west eroded depressions that might fill with water in wet years. 



The sandstone cliffs surrounding Billings are part of the 

 Eagle sandstone, called the Virgelle sandstone farther north. 

 Some researchers believe the sandstone is a barrier complex, while 

 others suggest it is part of an offshore, submerged bar. Whatever 

 the exact origin of deposition, the Billings rimrocks offer an 

 opportunity to study the sedimentology of this sandstone in 

 detail. 



The Crazy Mountains are an isolated mountain range north of 

 Big Timber. Driving along the Yellowstone River and looking 

 north, one can see the towering peaks resulting from alpine 

 glaciation. Along the east side of the mountains on the 

 Sweetgrass Creek and extending north into the American Fork of the 

 Musselshell River drainage are good displays of recessional 

 moraines, the hummocky or hilly deposits left at the toe of the 

 ice as the glacier was retreating. Moraines typically contain a 

 variety of rock sizes from clay to cobbles and boulders that are 

 jumbled together with very little sorting of the different 

 particle sizes. 



Surrounding the Crazy Mountains are a series of radial dikes 

 that radiate out like spokes of a wheel from the central diorite 

 stocks (igneous intrusions) near the center of the mountains. The 

 dikes cut through the surrounding sedimentary rocks and stand like 

 walls over the surrounding terrain. This is one of the best 

 examples of a radial dike swarm in the country. 



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