I once camped near there on Devil's Path. I didn't know that camping within 30' (I think) of a trail is illegal. A ranger pulled me out of my tent at around 10pm and ticketed me. I later learned that she also continued to hike along the Path all night till dawn, IN THE RAIN, and ticketed several other campers. If you know the area and it's terrain, the other thing is that if you move 30' away from the trail, there's basically nowhere suitable to pitch a tent. You might be able to make a hammock work though.
I have a friend who camped at Echo lake. He wouldn't have done so if he thought it was illegal and I trust him for this type of nature stuff. I would go for it if I were you. Most places where you would want to camp but are not allowed to specifically say it is prohibited in my experience.
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