I know exactly the lake you’re talking about. I used to fish it often when I lived in Kalispell. I always did well there for both species with a balanced leech and a chiro dropper under an indicator near the creek mouth.
Is that the San Rafael Swell/Boulder Mtn/Torrey area? I've seen petroglyph panels similar to these, but it's been probably 30+ years and my memory is a little foggy.