No reservation required to use mountain trails, or to walk around observatory. But the observatory itself i believe is closed at this time.
Trails are open all the time and do not require reservations. The Observatory is closed right now, but when it is open, you don't need reservations to go in and see some free exhibits, but there are also things inside that you need to buy tickets for. Parking is limited depending on the area and just read the signs because some areas are dawn until dusk, and some of the parking areas are open until 10pm. The parking area next to the Observatory costs money, but you can park on the road leading up for free, or down by the Greek theater and hike up for free.
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