[FarmerJohn1324 (OP)]

Hey Guys.

Here's something I was wondering.

How can the crust be thicker in eastern Canada (the craton) than it is in the Rocky Mountains even though the elevation is so much higher in the Rockies?

[JimBob]

Contours are in kilometers - (map from USGS)

It isn't, really. The less than 30 kilometer thickness in southernmost Rockies in Canada and south into the US is due exclusively to the extensional forces that are causing the Basin and Range province. This crustal extension is the result of an only partially understood process that is probably due to a "stuck" subduction plate that many geologist think is causing a rise in the crust resulting in the sudden elevation of the Colorado Plateau in the last 5 million years.

The whole "extensional debate" subject is a VERY long discussion.