I read this collection of essays, originally published in 1992, with a very specific agenda. I'm in the early stages of working on a book about the "Rocky Mountain intellectual tradition" (phrasing may change). So it was striking to me how little attention the writers give to the states that occupy the time zone, an imperfect definition, but good enough for a start. Sara Deutsch's essay on race in the West begins with a fascinating sketch of the Hispanic enclave of Greeley, Colorado; John Faragher's "Americans, Mexicans, Metis" juxtaposes New Mexico and Quebec; D.Michael Quinn's survey of religion incorporates Utah's Mormonism. There's a bit about gender in mining and logging communities, but not much else. (I started by checking the index, which presented an even bleaker picture; turns out the index isn't particularly well done.)
So. If you want the Rockies, the interest is limited.
For the West as a whole, it's a useful point of reference, one very much grounded in the moment of its publication, which results in an interesting tension between backward-looking and forward-looking historical approaches. The "backward" part is reflected in the drumbeat of references to Frederick Jackson Turner's "Frontier Thesis" specifically and the myth of the frontier more generally. By 1992, the historical consensus had definitely reduced Turner's vision of the frontier as the cradle of democracy from fact to myth. Nonetheless, as many of the essayists reflect, that myth played and continued to play a shaping role in the history of region and nation; see Barry Goldwater and Ronald Reagan for details. Patricia Limerick's discussion of Henry Nash Smith's Vigin Land as a germinal text in American Studies and Western history does a great job of showing how the Turnerian approach resonates in fascinating ways. The "forward" part of the mix comes through clearly in the essays advancing a more diverse vision of regional history: Deutsch and Farther on race; Deutsh and Katherine Morrissey on gender. In the years since the publication of Under an Open Sky, numerous historians have responded to the calls of those essays, which means readers grounded in that history are likely to nod and say "of course" without learning a lot new. Not a failing of the book, just more evidence of how time changes reading.