Help me plan a trip to AZ with a six-year old

We will be staying in Scottsdale, but will rent a car.

My boy is almost seven and I should point out that he has a very unusual interest in all things scientific and he is crazy about cacti. He also wants to go hiking.

We will be there for three full days.

I was thinking about possibly seeing Meteor Crater and Colossal Cave. How long does it take to drive to these places from Scottsdale?

Any other suggestions? We will be the March 21st to 25th.


Loads of it.
Other than that, I know nothing.