File:Flickr - …trialsanderrors - Ruby Canyon, Colorado River, Colorado, 1900.jpg

59026. Citadel Walls, Canon of the Grand, Utah. Photochrom print by the Detroit Photographic Co., copyrighted 1900.

The original title of this postcard is "Citadel Walls, Canyon of the Grand, Colorado River, Utah", but it seems this is Ruby Canyon, just inside Colorado. The Grand Canyon is in Arizona, not Utah, so the "Canyon of the Grand" must refer to something else. It turns out that the Colorado River, between its source and its confluence with the Green River, used to be called the Grand River, so this seem to be the Canyon of the Grand [River]. The railroad that follows the Colorado river (mostly on the north shore, so we're likely looking east) is the Denver & Rio Grande Railroad (map), which turns off just west of the Colorado-Utah border. So we're down to a very short stretch of the river and have to look for a location where the railroad tracks are wedged in between river and rock, with a distinctive peak between two valleys. If this particular rock formation is called Citadel Walls, I don't know.

Today, the line is part of the Amtrak California Zephyr line, which means I've seen this place before.

From the Photochrom Prints Collection at the Library of Congress More photochroms from Colorado & the United States | More photochrom prints