My most favourite being the attribution of these
structures to "prehistoric Masons". The classic text
(with beautiful engravings)is
E.G. Squier and E.H. Davis. Ancient Monuments of
the Mississippi Valley: comprising the resultsof
the extensive originial surveys and explorations.
1848.
And for a short, sweet simple overview (and a bibliography
which may give you some other leads), I blush to suggest
Maureen Korp. The Sacred Geography of the American
Mound Builders. 1990
best wishes,
Maureen Korp, PhD
University of Ottawa
mkorp@uottawa mkorp@acadvm1.uottawa.ca