I figured you'd get numerous responses by now. Park rangers can use many different types of radios depending upon where they are.
Having watched more movies and TV shows than I should, I can say almost always some kind of prop is used and most often is a regular hand-held scanner. "Non-scannists" won't see the difference and "scannists" always like debating what kind of scanner was used.
Even back in the late 60's Jack Webb who was a stickler for realism blocked out manufacturer names when they shot the control head for the police car radios.