The highway proceeds due east until reaching the unincorporated settlement of Mallard Bay, where it curves to the southeast to avoid the eponymous bay.

SH-251A curves back to the northeast, paralleling the short of Fort Gibson Lake, before reaching Fort Gibson Dam.

The route crosses the Grand River along the top of the dam, entering Cherokee County in the process.

[4] What is now SH-251A was originally added to the state highway system as part of a 1955 extension of SH-16.

[5] In 1965, SH-16 was realigned to head north from Okay instead of east, and the vacated section of highway was assigned the SH-251A designation.