Vietnam, North Korea, Cuba and - in the short term - a bunch of Native American tribespeople have also beaten the USA army

The Taliban has Guns and Mountains though

They also never relied on social media provided by US-based corporations (and with built-in back doors) for their organization and communications.

The Taliban did operate in a lot of open desert areas as well and had marginal success, I would assume that American people would be better armed than the Taliban and you'd probably see US military or National guard guys stealing and supplying the militia groups if it got serious. Look at Ukraine as well a lot of flat farmlands and Russia even with all of their equipment has a hard time pushing forward, and they just zerg.