This is from the early years of 20th century, probably in Arizona.
I am asking you folks because her clothing is rather unusual for a studio portrait. Tassled fez, riding boots, gaiters, fancy gloves, a canteen (?), and a pistol.
I've never seen the like, and am wondering if there's a cultural angle for the time. Is this a turn of the century genre, like (say) what a woman would wear if she were a Pony Express rider? Or some other kind of uniform?
Photo: https://imgur.com/Ud1gXg6
EDIT: Don't know that anyone else will look at this, but I'm not so certain anymore about the girls' identity. Removed my guess so no one is confused by it.
Gorsall's history of costume has a big western section. There was no uniform for Pony Express riders, and I never heard of a girl sneaking into their ranks, and I collect those kinds of stories.
This is riding gear, and the undivided skirt means she rode sidesaddle, making the gaiters to cover her legs more important. She would have breeches on under the skirt, tailored for riding aside (the buttons are not on the side of the right knee but on the front of the knee). (Mrs. Hayes, The Horsewoman, 1903). The Sears Catalogs sold Western stock saddles in the three-horn style for riding sidesaddle w/one tapadero.
I don't see any fancy gloves, but plain gauntlets.
As for the fez, that would strictly be her whim, perhaps for a zouave regiment touch. There was a fashion for exotica that shows up in theatre and opera, but in the home, too, as in the "Turkish corners" shown in Meyer's Once Upon a City.
She has a varmint pistol and a canteen. The thing I find odd is her being in a shirtwaist without a jacket for something so outdoorsy.