I believe this photo was taken by E. Burton Holmes
My guess, Yellowstone Riders from L to R:
1) Corp. John Wiliams
2) Sgt. Dalbert Green
3) Pvt. William Haynes
4) Pvt. Elwood Forman
5) Pvt. William Proctor
6) Pvt. Frank L. Johnson or Lt. Moss
7) Pvt. John Findley
8) Musician William Brown
Trying to identify the enlisted (i.e. black) riders has been an enjoyable challenge. As far as I know, nobody has attempted to do this. Moss, of course, is very easily identified in all the photos. Enough clues exist for the riders who made the Yellowstone trip that they can either be identified outright or be deduced by process of elimination. Below is my reasoning.
1) Corp. Williams identified in this photo in the book Black Regulars, pg. 109. In the Minerva terrace photograph his moustache can be seen. Although his hat brim is different in the two photos, zooming in on the photo reveals a stripe on his pant leg - which rules out Haynes, the only other rider with a moustache.
2) Sgt. Green -compare with Minerva Terrace photo and Philippines photo (Black Regulars, pg. 279). Note the slight beard, light complexion and heavy set
3) Pvt. Haynes - compare with Minerva Terrace photo. Note the mustache. (see comments on Williams
4) Pvt. Forman - compare with baseball photo in Nankivell's Buffalo Soldiers, pg. 165. Compare the round face and darker complexion. Forman's hat seems to have a much short brim, which he wears upturned, giving the impression, almost, of a Tyrolian hat. This is helpful in identifying him in other Yellowstone photographs.
5) Pvt. Proctor - compare with Minerva Terrace photo. Compare the crease in the crown of the hat (which is unusual in that it is perpendicular to typical fashion)
6) Pvt. Johnson OR Lt. Moss -this is mostly process of elimination. Compare with Minerva Terrace photo. Note the similarity in the way the hat brim is shaped and the way his equipment is packed on his handlebars. Could this rider be Lt. Moss? The shape of the hat looks a lot more like his than Johnson's (see Minerva Terrace photo). The shape of the face in the Holmes photo looks like Moss, too.
7) Pvt. Findley - note the tool box attached to handlebars, his height and complexion (light) in comparison with Minerva Terrace photo
8) Musician Brown -identified in Minerva photo by musicians stripes on his pants. Note the way his hat brim is folded back in both photos.
As I look at the different photos I am struck by the individuality of the hats. I think they aid greatly in identifying the men. Also, I've not seen a photo in which all of the riders appear. This is true for the Missoula-St. Louis riders. Is there some explanation for this?