It's my favorite place in the world, but they've got black bears that know how to break into cars. It's one of the few places in North America where that happens. I haven't gotten to the point yet where I've taken a child car seat there, but I remember the National Park Service would recommend that seats either be cleaned out or even taken out - because of the assorted food smells that might be trapped in the seat. That's definitely what's recommended in campgrounds, and I saw a few fellow campers with their car seats sitting on their picnic tables instead of inside their cars. The theory is that if bears can just explore one up close and personal, they'll figure that it's just a smell without any food. If they smell it inside of a car, they might just break into the car to explore what it is.
http://www.nps.gov/yose/planyourvisit/bears.htm
http://www.nps.gov/yose/planyourvisit/bears.htm
How to Store Your Food...
In your car
You may store food inside your car (out of sight, with windows completely closed) only during daylight hours. Do not store food in your car after dark: use a food locker. Remember to clear your car of food wrappers, crumbs in baby seats, and baby wipes. Even canned food and drinks must be removed from your car.