The following sources might be of further interest:

_Mark Twain and Orion Clemens_ by Philip Fanning, pages 203-204.
Fanning also references two articles by Fred Lorch that were published
in 1929 in _Iowa Journal of History and Politics_.

and

The newspaper article titled "The Fourth" in _Keokuk Weekly
Constitution_, July 7, 1886, p. 1 which details Clemens's
participation in the festivities and includes text of his speech
not recorded in Paul Fatout's _Mark Twain Speaking_.

and

from Lou Budd's check list of Mark Twain interviews:

"Amusing the Children / Thus Does Mark Twain Kill Time While In
Chicago." Chicago TRIBUNE, 9 Jul 1886, p. 1.
SLC discusses recent visit to Keokuk, scenery of upper Mississippi River,
and neglect of area by travel writers and social commentators; praises
steam boat travel.

Barb