This short explanation of the Mountain West Digital Library (MWDL) is a good introduction to this relatively unknown resource among family historians.
We provide free access to over 960,000 resources from universities, colleges, public libraries, museums, historical societies, and government agencies, counties, and municipalities in Utah, Nevada, Idaho, Arizona, Montana, Hawaii, and other parts of the U.S. West.However, you need to browse through the MWDL's extensive list of partners to appreciate the resources of this remarkable online record hub. As is the case with any library, you can only begin to appreciate the contents by browsing the shelves. In this case, a review of the digital collections will certainly stimulate your interest in the website.
For those who have ancestors who lived in the Mountain West, I suggest that this is a rich source of photographs and histories of the entire area. There are thousands of images that could be of major interest to you and your family.
In light of the upcoming dedication of the new Provo, City Center Temple on March 20, 2016, here is a photo of the Provo Tabernacle from 1900.