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Ten miles northeast of Dillon on Montana Highway 41.
The prominent geological feature to the northeast of where you are standing is called Beaverhead Rock.
Over 200 years ago on the afternoon of August 8, 1805, members of the Lewis and Clark Expedition brought their canoes up the Beaverhead River in the valley below toward the Continental Divide.
They sighted what Clark called a “Remarkable Clift” .
Sacajawea recognized this large promontory and told the them that her people called it “Beaver’s Head.”
In ancient times, a shallow sea covered much of Montana.
Billions and billions of tiny sea creatures thrived in the water and when they died their bodies settled into the deep muck on the ancient sea bed.
Beaverhead Rock is composed primarily of the hard body parts of these creatures which is called calcite and is made up of calcium carbonate; CaCO3.
Calcite is produced as marine organisms draw calcium carbonate out of the water in order to build thier shells or other hard body parts.
As these organisms die their soft tissues decay, but the shells, etc. made of calcite build up as sediment on the sea floor.
After about 10 million years of accumulation and many more millions of years of compaction this muck became the pale gray rocks of Beaverhead Rock that you see toward the northeast.
This type of pale gray rock is common throughout Montana, eastern Idaho, northern Wyoming, and in the Dakotas.
In Montana, these rocks range from 1,000 to 2,000 feet thick.
Many of these formations are seen today as spectacular cliffs and ridges that make traveling through Montana a scenic adventure.
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To earn credit for visiting and logging this earthcache, you must email me with your answers to the following six questions:
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1. Look at the rocks of Beaverhead Rock and the information on the nearby roadside geology sign.
What do you think the pale grey rock that forms Beaverhead Rock is called ?
For a close up view of this type of rock, look at picture "L" in the gallery.
2. From the information that you learned on the geology sign; About how many years ago did a shallow sea cover much of Montana ?
Extra Credit Geo Fun :
To get an idea of how long ago this was, take your answer for question 2 and divide it by your age.
This will tell you how many of your lifetimes this was !
3. Geo Fact:
About 70 million years ago a large batholith pushed up through other formations to form the Tobacco Root Mountains that you see on the horizon far toward the northeast.
What type of rock do you think this batholith is composed of ?
For a close up view of this type of rock, look at picture "G" in the gallery.
4. When limestone is recrystallized at high temperatures and pressures deep within the earth, a metamorphic rock is formed. (metamorphic means "change in form")
What is this type of metamorphic rock called?
For a close up view of this type of rock, look at picture "M" in the gallery.
(Hint: Also a name for something round. )
5. Geo Activity:
Lewis Clark and Sacajawea recognized Beaverhead Rock as looking like a giant beaver swimming on water.
From the viewing area, look all around and in every direction.
What names might you give to some of the mountains, rock formations or other geologic features that you see?
Thank You for Earthcaching 
Congratulations to MontanaNinjas for the first to find !