Take the job. You are already a world traveler, and this is an amazing opportunity to see parts of the US and Canada that people take for-granted. It would make a great portfoilio piece for you, and could potentially open up other opportunities while you're on the road.
I have a friend who did something similar out of college, nowadays he works in CO and spends most of his time doing photography to make a living, for groups such as Red Bull for their snowboarding tour, or for outdoor publications, etc. etc. And you know what? He's one of the most relaxed, down to Earth, and humble people I know. Everybody can travel to a monument or park and take a picture. Very, very few can do so while getting paid to be there.
Edit: Think I misinterpreted this a bit thinking it was specifically focused on Parks, but in either way, most of the points above still stand, I think. Unless that grant related project is super amazing.