>>14425814Much of the western US's land area was raised (up to 3km+ above sea level) from the ocean floor plate subduction under NA, while parts were subducted others were raised. It's plausible that a large chunk or layer of the rock record was stripped away and subducted with the ocean crust in certain areas or other geological processes worked to produce the same result. The rims of GC are 2000m (6600ft) and 2700m (8800 ft) above sea level respectively while the bottom of the canyon beneath those high points on the rims is as low as 750m (2500 ft). And although all of the mountain states in the US were raised to similar elevations (they are the most mountainous and highest average elevation states in the US and one of the highest in the world for its size, which is almost equal to all of Greenland in area) the GC is only of only a handful of areas where erosion stripped down into more than a mile of rock, so there are few other location to look for other unconformities elsewhere in the west to gather more clues and information.
