Pacific Ocean Park or POP as my Dad always referred to it as. I only saw POP in person once, that was in 1972 and it was very closed and very scary. It had been abandoned for years, partial burned down and was collapsing into the ocean. Obviously it had seen much better days. This 1959 Child Special Group Plan Admission Ticket was from from those better days. (cool inter-active web site)
I dig the Seahorse Logo, check out an old guide book full scan here.
This Junior ticket isn't dated, but I am guessing its newer than 1959, notice it's not on safety paper. Plus I think there are some of these still left to purchase, in fact I am sure of it. Check out Bob's Travels' current auction on EBay (link). I bought these exact ones your looking at from him. I've actually gotten some great deals from him, check his other stuff too!