It varies by state, but in the state of California, county, municipal, and local departments are at full risk. We have gear optimized for one or the other (Type 1 engines are geared toward structure fires, Type 3s are better for wildland), but we’ll use both at any incident that comes up. My first structure fire, my first interior attack, and my first time cutting through a roof were on a Type 3, and I went to my first vegetation fire in the backseat of a Type 1. If it has wheels and pumps water, you can work on it.
Federal agencies (US Forest Service, USBLM, NPS, and FWS) are wilderness areas only. That said, Forest Service engines often respond to structure fires on the basis of a “wildland threat,” even though they’re officially limited in what they can do (no interior attacks, no roof) , and they also respond with us. to traffic collisions and wildland rescues quite a bit.