A minor not for those here in the Midwest:

Many LIST-members may not be aware that here at St. Louis University, we
have the Cyril Clemens collection, which is quite extensive and
includes, among many other things, a tremendous number of copies of
letters, as well as newspaper coverage of Twain during the latter part
of his life.  And we do possess a fairly detailed listing of the
contents of this collection, although last I heard it is not on-line.
This collection also has extensive documentation of the early years of
Cyril's groundbreaking work to establish a national organization for the
study of his relative, Sam Clemens.