There is a $10 parking fee at the roaring camp in addition. It's totally worth it though.
There's a state park entry fee. The Roaring Camp Railroad trip up to the top of Bear Mountain and back is I believe $32 per adult and $26 per child. Besides the railroad there is a beautiful grove of redwood trees with a short hiking trail. There are also longer hiking trails, little shops, an eatery and lots of picnic areas if you want to spend the whole day there.
$10 for parking. Train is $32 for adult and $26 for children.
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