Roderick Nash, Wilderness and the American Mind (1967)
Nash traces American beliefs about nature and wilderness from their European and Biblically-based beginnings through the mid-20th century. Interesting and well-written, the book offers readers a grand overview of an important element within American ideology.
Jason Porterfield, The Homestead Act of 1862: A Primary Source History of the Settlement of the American Heartland in the Late 19th Century (2004)
This collection of primary sources brings the homesteading experience to life. It's not very extensive (only 65 pages), but it would provide a useful tool in the high school classroom.