Why are the interior plains so dry?

Question

My exam review says there are 2 answers for this.

1 has something to do with it being in the west

and 1 is in the name itself

thanks!

Answer 1

Wet air off oceans looses moisture over the ranges of mountains and has little moisture to contribute to rainfall on the interior plains. The Cascades in Oregon and Washington record 100 or more inches of precipitation each year, yet a few miles to the east 5-10 inches of precipitation fall! Each range of mountains takes a little more moisture out of the air, so places well inland tend to have almost no rainfall.