Library Search (Articles+Books+More) on the homepage includes the UW LIbraries' catalogs and articles from many databases. It's where I recommend you start your search. Additional databases to try:
Search Library Search for the names and locations of your civilization/culture. You may need to try alternate spellings, and you may find sources that only mention your group in a single chapter or for a few pages. Be sure to look at the Table of Contents and the Index.
Library catalogs and some databases use subject terms to bring together all the works on a particular topic, regardless of the words or phrases authors use. Unlike keywords, subject terms are not always intuitive. This is a list of selected subject terms related to Native American astronomy, archaeoastronomy, and other topics you'll be covering in your presentations. Try using them alone or in combination with each other or other keywords when you use Library Search.