There was skirmish on April 15 (some things are saying 18th) 2 companies of the 2nd Kansas and others were out foraging. Here's an account from the Fort Smith New Era (The Cook is Lemuel Cook, my wife's ggg uncle)

Last week a forage train was attacked by guerrillas about 10 miles below Roseville . The rascals rode into the camp dressed in Federal uniform and were quite sociable for a little while, till they commenced driving off the mules, when our boys found out what sort of company they had to deal with. A fight ensued in which 3 of our men were wounded' 1 mortally, and in which the leader of the rebels was killed. In his pockets was found his (rebel) commission and his Oath of Allegiance to the United States ; a journal of each day's occurrences and $75.00 in rebel money.—The fellow's name was Cook.

George Haas, 2nd Kansas, is the man that killed Cook. He took Cook's journal and made it own and backdated several entries. Here is the entry he wrote April 18 (I think his dates are off, especially since he was backdating):

“Stardet at 7 A.M. (5?) m down the River over went down 6 m. commenced pulling Corn at dinner was disturbed by 35 Bushwhackers firing into us. 8 men mounted after the 13th Kansas fired one volley they run, we followed them up 2 ½ m. Killed an officer, the owner of this book. Geo Spencer got wondet in the left thigh, got a (Beel’s?) revolver, shot gun, silver watch and $1000 Conf. bonds and the Oath of Allegiance went back to Camp. Went threw a town name Logan it ________ down I stardet with 16 men fo the 11th Cal went to Weathers go feather beds and 16 hams. Retirned to camp.”

I have a roster that says George Spencer was wounded April 4 in the action you mention, and another that he was wounded on April 15.