Why are some mountain rock layers turned sideways running vertically instead of horizontally?

Question

I was at Monticello Dam on Lake Berryessa in California and noticed the layers of rock were turned sideways. I thought the layers went down based on how old the rock was. What would make them go sideways like that?

Answer 1

This is due to the folding of the rocks. think of a piece of paper when you hold is horizontally in front of you and you apply force into the center (moving your hands towards one another) the paper folds into a 'loop'. When you are seeing the vertical rock layers you are seeing one of the limbs of the fold.

Answer 2

In this particular case, uplift and tilting along the plate boundary characterizes the structure of the rocks you are talking about.
The sedimentary rocks at Monticello Dam are late Mesozoic rocks of the Great Valley sequence deposited in a marine setting of a forearc. In the Putah-Cache Creek area, most of the Great Valley rocks are inclined (tilting) rather steeply to the east. They eroded to form a series of northwest-trending, east-dipping ridges of sandstone and conglomerate separated by valleys underlain by siltstone and mudstone. Water gaps in the sandstone and conglomerate ridges form this damsite and other proposed damsites. Uplift in the eastern Coast Ranges and tilting of the mountain front may be the result of buried (blind) thrust faults propagating eastward beneath the mountains.

http://bioregion.ucdavis.edu/book/06_Monticello_Dam/06_03_moores_geo_gvs.html
http://geology.about.com/od/geophoto_tours/ig/CAtransecttrip/stop5dam.htm
http://geology.about.com/od/geophoto_tours/ig/CAtransecttrip/stop5rox.htm
http://www.storage.water.ca.gov/docs/o_reg_geo_plate_faulting.pdf

Answer 3

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Answer 4

As Geologist has said folding is the most common cause. Faulting can also up end rock layers.

Answer 5

Earthquakes. Those layers are very old, and movements of the earth happen with some frequency in the western states. Over time they change position.

Answer 6

"geologist" has it! I was going to day "folding" because I just learned it this week. Earth Sciences is fascinating and exciting. Never stop learning. I am retired and now have time for scientific studies. Joy - Joy - Joy...