Seen from a satellite, this is what Diamond Lake looks like. You might say, “It isn’t diamond shaped. Are their diamonds here?” The answer is that there are no diamonds and it wasn’t named because of its shape.
Notice the two peaks, one on each side of the lake. The one on the left is Mount Bailey. The one on the right is Mount Thielson. Mount Thielson is the taller of the two and it really stands out when a person is at the lake.
The lake is named ‘diamond’ because of Mount Thielson. That might not make sense, but Mount Thielson is a very jagged and steep mountain. That earned it the nickname of “Diamond Peak”. Since the lake is at the base of Diamond Peak, it is called Diamond Lake.