The Grand CanyonThe Grand Canyon

Megan PickardMegan PickardTESSE 2009TESSE 2009

Law of Original HorizontalityLaw of Original Horizontality• Sediments are deposited in layers that are

horizontal

Law of Superposition:

• In layered sedimentary rocks

• Rocks on bottom are OLDER than rocks on top

• So…

Tapeats Sandstone520 million years oldTapeats Sandstone520 million years old

Kaibab Formation270 million years oldKaibab Formation270 million years old

http://mountaincatgeology.wordpress.com/2009/02/16/unconformities/

ANGULAR UNCONFORMITY

Volcanic Activity

• Began 630,000 years ago• Last eruption was around 400,000 years ago

One of many cinder cones that sit on top of the youngest sedimentary layer above the Grand Canyon

Lava cascaded over the rim of the Grand Canyon, damming the Colorado River at

least 13 times!

~2540 feet

• So which is older in the Grand Canyon: Basalt or Limestone?

http://www.nature.nps.gov/views/layouts/Main.html#/GRCA/geology/

• Uplift of the Colorado Plateau was a key step in the eventual formation of Grand Canyon. The action of plate tectonics lifted the rocks high and flat, creating a plateau through which the Colorado River could cut down.

• The Colorado River has been carving away rock for the past five to six million years. Remember, the oldest rocks in Grand Canyon are 1.8 billion years old.

• The canyon is much younger than the rocks through which it winds• Several factors increase the amount of downcutting that happens in Grand

Canyon: the Colorado River has a steep slope, a large volume, and flows through an arid climate.

• Gradient is a measure of slope. The higher the gradient, the steeper the slope. If you go sledding, a steeper slope means a faster ride down the hill. For riverbeds, a high, or steep, gradient means a faster current. A river with a faster current has the power to carry larger rocks and boulders.

• On its 277 mile (446 km) journey through Grand Canyon, the Colorado River descends about 2,000 feet (610 m) in elevation.

General Geology Notes: