This is a very old fashioned text you have found. I had never even seen the word guidon before and had to look it up.
Here is the definition of "range" that fits your example.
Range: Also called rangeland. an area or tract that is or may be ranged over, especially an open region for the grazing of livestock.
In the history of America during the time called Westward Expansion, or commonly known to us as the "Old West," the large grasslands or the lands where the cattle ranches were were sometimes called "the range." We don't use that term commonly anymore unless referring to that time period. At least, in my part of the country we do not; it could be that they use that term still in Texas. There's a famous old song you might check out called "Home on the Range."