Imagine a world very different than we know today. About 1.5
billion years ago during the Precambrian Era, the earth's
environment was desolate, with no tree, fish, animals or birds.
Shallow seas with extensive near-shore flats were fed by streams
that deposited great amounts of sand and mud. Rain frequently fell
and pooled in the vast shallow lakes and ponds in what would one
day become northwest Montana.
The Earth's crust slowly sank forming a large geologic basin in
which Belt Supergroup sediments accumulated. The rocks are common
in Northern and Central Idaho and Western Montana, and extended
east to the Little Belt Mountains in Central Montana. The
sedimentary rocks along Interstate 90 between Lookout Pass and
Alberton are almost entirely rocks of the Belt Supergroup. These
rocks are distinguished by brown, gray, red, green, purple, and
yellow colors and locally form dramatic cliffs where resistant,
well-cemented sandstones are exposed in the canyon.
Interstate 90 from near Lookout Pass through Missoula is located
along the Lewis and Clark Fault Zone, a series of faults that
stretch between Northwest Washington State and the Helena, Montana
area. The faults had significant movement about 70 million years
ago when the Rocky Mountains were uplifting and were active until
at least 25 million years ago. Interstate 90 and US Highway 10 in
Western Montana follow the trend of the faults along the straight
canyons that eroded along the fault zone.
Resources: Signage at the posted
coordinates.
To claim this Earthcache you will have to answer the
following questions and email me (AmplePeach@gmail.com) the
answers. Please do not post answers in your log, If answers are
posted, your log could be deleted without warning. Make sure to
post a photo if you can. Thanks!
1. Visit the information center at the
above coordinates. The answers to questions 2 & 3 & 4 can
be found here.
2. Blue-Green Algae mats often trapped
what type of particles?
3. How many years ago did the Earth's
crust sink? How many miles thick did the sediments accumulate?
4. Ancient rocks indicate that oxygen
was not abundant in Earth's atmosphere until how long ago?