I read through a book a couple or three years ago called The Annals of the Former World by John McPhee. I didn't realize just how much I had learned when I read that book.
During this last week, a friend of mine posted a picture on her blog (as she is wont to do) that I recognized immediately as Basin & Range topology. Basin & Range? I'll explain shortly - but first ... I asked her where the picture was taken. She said "Death Valley". Death Valley is in the northern reaches of the Basin & Range topology of the American Southwest.
Like I said, I learned more than I realized when I read the book.
The Earth's crust in the Southwest is thin. Rifting occurred sometime in the ancient past (and may still be happening) that created the Basin & Range topology that is so distinctive - alternating basins and ranges of hills and mountains - where the land slopes from the backside of one range down to the face of the next range.
This rifting and stretching of the earth's crust allowed superheated ground water to deposit gold and silver near the surface in quartz deposits. This fact enters into the book I'm working on - land that Sarah inherits from Jake Bertrett is found to be rich in precious metals. It's this thinned crust that is the source of the precious metals.