Headshot of James Patrick Majors in uniform in order of battle Wilson's Creek, in J B Clark's 3rd Division
Jim McGhee has him as 1st Cavalry Battalion, Lt. Col. James P. Major (Raised to 1st Regiment) then 1st Cavalry Regiment, Col. James P. Major here: https://mogenweb.org/mocivwar/confederates.html
It appears to me that Majors was a Lt Col with the 1st Cav Battalion at Carthage serving under Col William Brown. His unit with Rives was in an ineffective blocking location when pushed aside by Siegel as the Union forces withdrew south into Carthage proper. He then appears at Wilson's Creek a month later as Col commanding 1st Cav Regiment.
In Michael Banasik's Confederate Tales of the War in the Trans=Mississippi, page 127 a foot note reference relates the following:
"James Patrick Majors was born on May 14, 1836 in Fayette MO. He attended West Point, class of 1852, graduated number 23 of 49 in 1856. After serving on the Texas Frontier fighting Kiowa and Comanche Indians, Majors resigned from the Army March 21, 1861 and joined Earl Van Dorn's staff at Wilson's Creek. (after I think) At Wislon's Creek Majors commanded the 1st Cavalry Battalion, 3rd Division, MSG. Majors later transferred east of the Mississippi River where he served for a time as Van Dorn's Chief of Artillery. On July 21 1863, he was promoted to brigadier general....Warner, Generals in Gray, 209-10, ..."
During the Red River Campagin he is leading a Texas Cav unit. Post war he lived in France then returned to Texas as a planter, died May 7, 1877 in Austin Texas.
So a north central Missouri native graduate of West Point with horse combat experience hooks up with Poindexter in SW MO in time to be leading at least one company, Co A, at Carthage in early July 1861, lands a larger command at the time of Wilson's Creek a month later. At least members of his Unit end up at Lexington 1 in September. In 1862, not sure if he is there, moves east when MSG is enrolled in CSA and works for Earl Van Dorn. Apparently competent in a workman sort of way survives the war becomes a Texan.