Rosso,
As a long time resident of Wyoming I can say definitively that there was not a stick of common-carrier narrow gauge in this State, surprisingly enough, even though our neighbor to the south, Colorado, had a couple of thousand miles.
That being said, two famous names in 3' gauge circles, the Fremont, Elkhorn & Missouri Valley and the Colorado and Southern met and interchanged at Orin Junction, Wyoming. Both of the lines of these companies were Standard Gauge.
Yes, I can remember the narrow gauge of the Laramie Tie Plant. but that was strictly within the company for treating ties and was shut down when the creosote bloom began contaminating the Laramie River,
Rick