The Natives of what is now the Southeastern US had a very rich cultural heritage before European contact. Much of that was not recorded prior to the radical changes that contact brought about. There are some good sources of information that can be gleaned from the folklore, tales, and legends that have been collected by Ethnographers, however. Some good resources for that information are:
Swanton, John R. Myths and Tales of the Southeastern Indians. Norman, OK: University of Oklahoma Press. 1995. Originally published in 1929 by the Smithsonian Institution as Bureau of American Ethnology Bulletin No. 88.
Lankford, George E. Native American Legends: Southeastern Legends: Tales from the Natchez, Caddo, Biloxi, Chickasaw, and Other Nations. Little Rock: August House Inc. 1987.
Mooney, James. Myths of the Cherokees. Dover: Dover Publications. 1996 Originally published in 1888.
Mooney, James and George Ellison, ed. James Mooney’s History, Myths, and Sacred Formulas of the Cherokees: Containing the Full Texts of Myths of the Cherokee (1900 And the Sacred Formula). Bright Mountain Books, Inc. 1992
Brown, Virginia Pounds, and Laurella Owens, eds. Southern Indian Myths and Legends. Leeds AL, Beechwood Books. 1985.