Okay, I've kept up with this thread, but haven't had time to post any information about the sources that might help you, until today. A lot of the research I did for Facets might come in handy.
Ute Tales. By Smith, Anne M.; University of Utah Press, Salt Lake City.
ISBN 0-87480-442-6.
-This is a collection of Ute Indian folklore and fairy tales.
-I pulled the Tsiants (the Ute version of ogres) directly from this book.
Island in the Rockies: The Pioneer Era of Grand County, Colorado, to 1930. By Black III, Robert C.; Grand County Pioneer Society; Country Printer; Granby, Colorado.
Library of Congress Cat. No. 70-80767.
-Mostly useful as an authoritative text of the conflict between the Utes and the settlers.
-Probably limited utility for your needs.
Web sites:
Native American Legends and Folklore
http://www.native-languages.org/legends.htm
-Probably the single most useful
-A great central repository with scads of links
Indigenous People dot net
http://www.indigenouspeople.net/
-Lots of stories from indigenous people from throughout the world
-Not just limited to American Indians, although the selection of those stories is pretty impressive, too.
American Folklore dot net
http://www.americanfolklore.net/index.html
-The selection of indigenous stories isn't nearly as good, but it has a fair smattering of 19th Century American tall tales
-Limited utility for me, but you might get more out of it
If you're looking for some more fictional and dramatic examples of stories based on American Folklore, I can't recommend Manly Wade Wellman highly enough:
https://en.wikipedia.org/wiki/Silver_John
For horror with a Caribbean flavor check out
http://www.miaminewtimes.com/1997-06...hs-over-miami/
If you can't find inspiration in those children's stories, turn in your GM's hat. The provenance of those stories might be a bit questionable, but as sources of inspiration they're tough to beat.
At one point, you mentioned voodoo and asked if there was anything else like that. I haven't seen you mention Santeria, yet, so I don't know if that interests you.
This is a good overview:
http://www.aboutsanteria.com/what-is-santeria.html
In Facets, the practitioners of Voudou and Santeria seek assistance from the spirits, which usually demand sacrifice of some sort. Generally, for a spirit to work its will in Assiah, it needs intermediaries which, in some cases, act as "chevals" or "horses," for the
loa ("lawgivers") to possess.
This is dangerous, as the spirit tends to like to "rearrange the furniture" in the mind of the cheval, to make it more amenable. The more a cheval gets ridden, the more his or her personality begins to resemble that of the spirit (in GURPS terms, the psychological disads and advantages get acquired or swapped around).
Eventually, if a cheval gets ridden too much, the original personality disappears completely, and the body just becomes a "glove" through which the spirit works its will upon the world.
The whole notion of losing one's mind is seen as wholly unacceptable (or even horrific) by the Cabal lodges. As such, they focus on manipulation of the decans, directly, and tend to react to the presence of Voudou and/or Santeria practitioners with suspicion -- or outright hostility.
The Columbine Lodge in Denver is a bit of an exception, because the loss of the occult library, early on, severely limited the power available to them. As such, they had to reach accommodations with the priests and priestesses of Voudou and Santeria, as a way to resist as a common enemy those who used the KKK as proxies.