Per ORN, I, 27:188 Mound City was still active as late as May 8, 1865 when she participated in a mission up the Big Black River. Here is a link to the electronic ORN citation.
<http://cdl.library.cornell.edu/cgi-bin/moa/pageviewer?frames=1&coll=moa&view=50&root=%2Fmoa%2Fofre%2Fofre0027%2F&tif=00220.TIF&cite=http%3A%2F%2Fcdl.library.cornell.edu%2Fcgi-bin%2Fmoa%2Fmoa-cgi%3Fnotisid%3DANU4547-0027>. She was also on the Red River campaign the previous year.