The action in Martinsburg by Cobb occurred on the 18th the day after the "Fulton Races" . It occurred in Audrain County and involved only Cobbs Company of State Guard Cavalry and two Union Officers, Major Benjamin Sharp newly commissioned to raise a Regt of Union Forces in Audrain, Callaway, Montgomery and Pike Counties and a Lietenant A. Yager of Melters Union Company of St. Louis. Sharp and Yager were on their way to Mexico. Missouri and were ambushed at Martinsburg by Cobb, who had observed them in the Whetstone Area of Callaway County after the two Union officers became lost, he got his command ahead of them and ambushed them near the Audrain/Montgomery line but effectively killed them and disposed of the bodies in Audrain County.

Reference for that action is : History of St, Charles, Montgomery, and Warren County Missouri. St Louis National Historical Company 1885.