Pikes' first exploration was the Mississippi river.
Step-by-step explanation:
Zebulon Pikes was in the position of brigadier general in America and discoverer. Under Thomson Jefferson’s (3rd president) authority, Pikes led the two expeditions. First expedition took place in the period of 1805 to 1806.
This was to examine the Mississippi river’s northern part in the upper level which was the newly established Territory Of Louisiana. Also, to throw out the unauthorised trading occurrence by fur traders of Canada at U.S border regions. Then, reached the river on Sep 21 and purchased Fort Snelling. In addition, further proceedings did to made a winter camp at Swan river side.