From peculiar circumstances I was able to identify them.
** Robert Brewster Stanton explained this very clearly in his investigations for the Canadian Pacific Railway into the causes of land-slides on that line.
In the basin of the Colorado are found in perfection all the extraordinary conditions that are needed to bring forth mammoth canyons.
The headwaters of all the important tributaries are INVARIABLY IN THE HIGHEST REGIONS and at a long distance from their mouths, so that the flood waters have many miles of opportunity to run a race with the comparatively feeble erosive forces of desert lands.

The main stream-courses are thus in the lower arid regions and in sedimentary formations, while their water-supply comes from far away.

The deepest gorges, therefore, will be found where the rainfall is least, unless diminishing altitude interferes.

Thus the greatest gorge of the whole basin, the Grand Canyon, is the one farthest from the sources of supply, and in the driest area, but one, of the whole drainage system.

It ends abruptly with the termination of the high arid plateau which made it possible, but had this plateau extended farther, the Grand Canyon would also have extended a similar distance.