There are 'hidden Z's' throughout...hit one and its good for 100,000 pts (happened to me twice, my son once during our August trip).
Hitting the volcano is good for 50,000 pts.
Generally, hitting Z's farther away earn you greater points.
Once I'm able to determine which 'laser beam' is mine, I'll try and key on a target, hit it, then hit it repeatedly a few times to boost the score.
I've always come out of there with 200-300,000 points...my family insists I cheat and it annoys the heck out of them, since they're lucky to break 50,000!