Parking is on one of 2 dirt pullouts near the
erratic.
Two characteristics largely define a
glacial erratic. First is that it must be
transported a significant distance by a glacier or iceberg. And
second, the erratic is typically a different rock than the
surrounding rock that it is deposited on. Size does not define an
erratic.
A glacier erodes large rocks and boulders and
incorprates them into ice. As the glacier moves, the rocks and
boulders move with it. When the glacier retreats, the ice
melts leaving the boulder behind, a glacial erratic.
The granite boulder on the road to Inspiration Point is
noticeably different than the surrounding rhyolite. With a bit of
searching, other boulders of granite can be found on both sides of
the canyon. Granite bedrock is not found anywhere near the Canyon
area. The closest granite is about 40 miles to the north in the
Beartooth Mountains.
Other evidence from the surrounding region shows that glaciers
covered this area approximately 14,000 years ago. The well-rounded
edges of the boulders and the distance from their source indicate
that a glacier transported these boulders.
Even though glaciers move very slowly, they are powerful
mechanisms for erosion. As you can see they can pick up large
boulders and transport them long distances. When the glaciers melt,
the material it was transporting is simply dropped.
Logging requirements:
Send me a note with :
- The text "GC14G64 Yellowstone Glacial Erratic" on the first
line
- The number of people in your group.
- Send me a note with the approximate height and width of the
boulder. Overachievers can lookup the density of granite and
include the approximate weight of the boulder
and/or
- Besides the difference in rock type, what features of the
boulder make it an erratic?
- Post a picture and coordinates of another glacial erratic along
the rim of the canyon (STAY ON THE TRAILS AND OBEY ALL HIKING
RESTRICTIONS)
The above information was compiled from the
following sources:
- Fritz, William J., Roadside Geology of the
Yellowstone Country, Mountain Press Publishing Company, May
1989.
- Canyon Area Trail Guide, Yellowstone National
Park, Yellowstone Association, April 2007
Placement approved by the
Yellowstone National Park