|Ok, the following is from The War of the Rebellion: a Compilation of the Official Records of the Union and Confederate Armies, volume 29, Part 1, page 494.
OCTOBER 22 1863.---Affair near Annandale, Va.
Report of Col. Layfayette C. Baker, First District of Columbia Calvalry.
NEAR ANNANDALE, VA., October 22, 1863
SIR : This morning about 10 o'clock a detachment of my battallion, under command of Maj. E. .J. Conger, and a detachment of the California battalion, under command of Captain Eigenbrodt, entered a squad of Mosby's men some 3 miles this side of Fairfax Court-house and near the Little River turnpike. One of Mosby's men (named Charles Mason) was shot and instantly killed. The celebrated guerrillas, Jack Barns, Ed. Stratton, and Bill Harover, were captured and forwarded to the Old Capital Prison. These men state that they were looking for government horses and sutlers' wagons. None of our Force were injured.
I am, colonel, your obedient serveant,
L. C. BAKER,
Colonel, Commanding First District Cavalry.
Lieut. Col. J. H. TAYLOR,
Scans of The War of the Rebellion is available online from Cornel University. I did a simple search for First District of Columbia Cavalry and this is what turned up:
I also did a search for Everton Conger, but got nothing. However, When I searched for just Conger the results considerably more:
I suspect the Major E. J. Conger in the above letter is probably Everton Conger. Anyway, I'm gonna link you to Cornel's main page for The War of the Rebellion. Should hopefully prove helpful.