Arizona State Geologist, Lee Allison, notes on his blog that the New York Public Library has placed about 40,000 historical stereograms online. About 196 of these are from Arizona (see here). A stereogram is a pair of photos taken from slightly different positions, which, when viewed properly, can produce a 3D effect.
If you go to the site, you find a gallery of photo pairs. Click on one to see it larger. Another click will make it even larger. With practice, you can see the 3D effect even without a stereo viewer. Try it with the medium size (one click from the gallery) photo pair. Here’s how. Instead of focusing on the computer screen, defocus your eyes and look behind the screen or cross your eyes. Move your head around a bit and the photos will coalesce into a 3D image. I have a practice photo pair below. If that doesn’t work for you, go back to Allison’s blog and click on the “stereogranimator.”