This truly is a treasure. I'm glad it has been protected for future generations. If you go back to fold3 and click on "Unit Information" for the 13th Battalion, you will find a report for March and April, dated April 30, 1863, showing their station as Aberdeen, Mississippi. (That doesn't necessarily mean the entire time was at that station, but that they were there as of April 30.) However, it is likely that when the first note was written, that is where they were. The Official Record has an account of the next action in which they took part. This is likely what he was anticipating, and later confirmed. Click this link and look near the bottom of the page for the action report of Major W.A. Hewlett, continuing on to the second page.

http://ehistory.osu.edu/osu/sources/recordView.cfm?Content=036/0691

Also see the following:

http://ehistory.osu.edu/uscw/features/regimental/alabama/confederate/alcav.cfm#13th-Cav-Bn

And the following:

http://ehistory.osu.edu/uscw/features/regimental/alabama/confederate/alcav.cfm#56th-Cav