WHAT? Brass remembered I had his copy of Rollins "The Cowboy" - man, now I'm goona have to buy my own copy.
Philip Ashton Rollins was born in 1869 of wealthy parents in the east who sent him west to their Montana ranch (which extended from Helena to the border of what is now Glacier National Park - that's big) each summer as a youth where he learned to cowboy and from all reports he loved it. Later trained as a historian at Princeton (BA and MA), he wrote a book of his experiences and knowledge that was published in 1922. His prose is that of an educated man, and contrasts with Abbot's work. Both are outstanding primary resources that compliment each other. In reading both, my impressions is that Abbot tends to cover the 1870's and 1880's while Rollins work speaks of the late 1870's thru the early 1890's.
Commenting on hats Rollins wrote:
"In the southwest, the crown was left at its full height, but its circumference above the summit of the wearer's head was contracted by three or, more commonly, four, vertical, equidistant dents, the resembling a mountain from whose sharp peak descended three or four deep gullies. In the northwest, the crown was left flat on top, but was so far telescoped by a pleat as to remain but approximately two and a half inches high.
"Few men of either section creased their hats in the manner of the other. A denizen of the Northwest appearing in a high-crowned hat was supposed to be putting on airs, and was subject openly to be accused of "chucking the Rio," vernacular for affecting the manners of the Southwesterners, whose dominant river was the Rio Grande. Present-day Northwesterners, faithless to this tradition, have foresworn the low crown and assumed the peak. The United states War Department recently has flown into the face of history by formally designating the dented high peak as the Montana Poke."
from 'The Cowboy', by Philip Aston Rollins, University of Oklahoma Press, 1997, p. 103
So what is this primary source telling us? First we are not sure what he means by 'southwest', my impression is that he is including west Texans. Did the Northwest then include Montana to the Oregon country. Assuming that, it would appear that the "Montana" peak originated in the "southwest" and not the northern plains where it would seem it was adopted along with the flat hat - where a high crown hat was trying to affect the appearance of the Rio Grande country. Further, the implication is that it was the US army that officially branded the name of "Montana Poke" on the style (although they may have stolen a popular expression of the period). As Rollins was basically describing the clothing of a cowboy of the 1880's and later we are probably safe in dating the design to that period.
This is the only primary source text I am aware of concerning the Montana Poke and it is noteworthy that writer attributes is first use to the southwest to be later adopted by the northwest cowboy.