A good source of Navajo County History can be found on the counties official website:

Navajo County Website

From the White Mountains Online website:

Navajo County Profile

These photographs are from the Library of Congress FSA-OWI and were taken by Russell Lee in 1940.
Photographs in this collection were taken by photographers working for the U.S. Government. Generally speaking, works created by U.S. Government employees are not eligible for copyright protection in the United States.
For more information: http://memory.loc.gov/ammem/fsahtml/fahome.html

Click on thumbnail to see a larger photo: