You might be wondering why a English 431 student would consult subject encyclopedias and other tertiary sources. The quick answer is that it can't hurt to make sure you have a good sense of how your research question fits in with other scholarly research that has been done--and the bibliographies at the end of encyclopedia articles are an efficient way to make sure you know who the scholars are who've been working on this topic.
The sources listed below are good starting points for developing context for your project. Remember that tertiary sources are intended to fill in gaps in your knowledge or jumpstart your research; they should not be cited as scholarly secondary sources.
The Cambridge history of the native peoples of the Americas by 
Encyclopedia of United States Indian Policy and Law by 
The Gale Encyclopedia of Native American Tribes by 
Handbook of North American Indians by 
Indians of the North Pacific Coast: studies in selected topics by 
A Guide to the Indian Tribes of the Pacific Northwest by 
A Native American Encyclopedia: history, culture, and peoples by 
Treaties with American Indians: an encyclopedia of rights, conflicts, and sovereignty by 