It is a county Park. You do need to reserve it for a day such as Easter. Start here: http://parks.lacounty.gov/san-dimas-canyon-community-regional-park/
Hi... I believe it's a county park, so you would need to call the them. If I'm wrong and it's a city park, you'd need to call the them. But be prepared, it's a full house on that holiday...:)
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