Dillon Pinnacles EarthCache
Geocaching HQ Admin: It has now been over 30 days since Geocaching HQ submitted the disabled log below and, unfortunately, the cache owner has not posted an Owner maintenance log and re-enabled this geocache. As a result, we are now archiving this cache page.
More information in the Help Center
-
Difficulty:
-
-
Terrain:
-
Size: 
(not chosen)
Please note Use of geocaching.com services is subject to the terms and conditions
in our disclaimer.
Site is at a pull-out on Highway 50 in Curecanti National
Recreation Area. Fully Handicapped accessible. No fees associated
with this site.
During the Cenozoic era, approximately 26 to 35 million years ago,
the area that is now Western Colorado was subjected to extensive
volcanic activity. None of the volcanoes that existed then are
present today, but evidence of there existence is all around. When
a volcano erupts to the extent that it empties its chamber and
collapses, it forms what is called a “caldera”. Southwest of the
Dillon Pinnacles, the remains of a caldera which was uplifted by
the Gunnison Uplift can be observed. The caldera now forms the
peaks of the rugged San Juan Mountains, such as Uncompahgre Peak –
the sixth highest peak in Colorado. Volcanic activity in the West
Elk Mountains, to the north of Dillon Pinnacles, covered this area
with volcanic ash and lava. This lava, along with mud flows, ash,
and rock fragments, formed a sedimentary rock called “breccia”. The
West Elk Breccia settled at a depth of approximately 600 feet over
the harder igneous and metamorphic rock of the Dillon Pinnacles.
The breccia is composed of hardened molten rock (magma) “clasts”
and an ashy material called “matrix”, formed by the mud flows and
ash, that cement the clasts together. The volcanic activity of the
San Juans to the south later covered this area with incandescent
ash which retained sufficient heat to fuse together and form a hard
“cap rock” over the tops of the mesas in this area. The harder
igneous rock clasts and “cap rock” are more resistant to erosion
than the ashy matrix of the breccia. The result is the formation of
the interesting spires and pinnacles of Dillon Pinnacles.
To claim this cache you must email me the answer to the following
question which is addressed by the interpretive sign at the
coordinates: What is the scientific name of the “cap rock” that was
formed over the mesas of this area by the incandescent ash deposits
from the San Juan volcanic activity?
Additional Hints
(No hints available.)
Treasures
You'll collect a digital Treasure from one of these collections when you find and log this geocache:
Loading Treasures