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Big Ambejackmockamus Falls EarthCache

Hidden : 10/01/2007
2 out of 5
2 out of 5

Size: Size:   other (other)

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Geocache Description:

This cache was originally placed by Northwoods Explorer.

This earthcache brings you to one of the most beautiful and heavily used sections of whitewater rapids along the West Branch of the Penobscot River. Did you ever wonder why the river in this section is so straight?

This earthcache will give you some insight into how the river has been shaped in this section. If you look on a map of this section of Maine you will see that the course of the Penobscot River runs very straight with the exception of two locations, the Cribworks and Big Ambejackmockamus Falls. The 11.5-mile stretch of river from Rip Dam to Abol Bridge drops about 310 feet in elevation with a major road running along its south shore for much of the distance. The river has easy access provided by the road and cold water provided by the dam year round. This section of river averages about 200 feet wide, and offers some of the states best fishing and whitewater boating.

In the 1980’s, the Great Northern Paper Company, owner of Rip Dam at the time, planned another dam here called the Big A Dam for electrical generation. One of the major objections at the time was that the dam would be built on a major fault. This fault might cause the dam to break and flood Millinocket down stream. Most people don’t think of Maine as having any major tectonic activity because Maine is now relatively quite in geological terms. The state is distant from sites of tectonic activity, which are distinguished by volcanoes, earthquakes, and other geologic events. Maine does experiences a few small earthquakes every year, but most are too small to be felt and do little if any damage.

The river in this section follows what is called the West Branch Fault, which has not moved in 385 million years. At the Cribworks the river takes a quick, short turn to the northeast. It once again takes the same type of turn at Big Ambejackmockamus Falls. These turns are caused by strong sets of fractures oriented at right angles to the West Branch Fault. These fractures were formed more recently but still 365 millions year ago. At Big Ambejackmockamus Falls you can see where the water takes a turn and once again turn as it pours over the edge of the fault once again joining the West Branch Fault on its trip down stream to Abol Bridge.

So while the glacier gave the final touches to the shape for the river as well as adding many rocks to the area, its general path came from fault activity much earlier in geological time and the water just followed the path of least resistance. It was formed at a time when Maine was tectonic activity, with volcanoes, earthquakes, and other major geologic events going on all around.

Remember this is an earthcache and there is no container just an educational activity. To log this Earthcache: You must send me the answer to the following question through my profile: At the posted coordinates you will be standing on a rock that is overlooking the river. As you look at the rock formation please take the time to see if you can explain why it has the unique shape that it does. Please begin your e-mail with the name of the earthcache and make sure your log includes the number of people in your group. It also would be nice if you would post a photo so others would know what they have to look forward to at this earth cache.

Please use the parking lot and do not park along the road where the signs say no parking. This can be a very busy area so please be careful while turning into the parking lot. To find the location just follow your GPS, if you would like to see the falls close-up just use your ears and follow the sound of the water as it tumbles over the falls.

If you enjoy this earthcache you may want to check the Maine Geological Survey located at (visit link)
They have developed a number of information sheets or field localities giving a great deal of information about geologic features. They also have a number of books and maps about Maine’s natural history/ geology that you might find interesting.

Additional Hints (No hints available.)