Jeff Cousins said:
We spent one night at Castaic Lake a few years ago and won't be going back.
We arrived late and were put in the rear row of the park. Very tight and low branches that made maneuvering our class A a real challenge. Also our neighbors were permanently occupying old, old trailers because they obviously couldn't afford anything else.
Not a great stay!
Well -- so much for my recommendation, Jeff. :-\

Guess I will have to update my mental files. A lot of parks will have that situation (sites left that they want to rent, but don't until everything else is gone). They "should" let you know up front that that is what is going to happen -- and some do, some don't. I know of many parks that have a "Monthlies" area -- and if there are some vacancies in that area, will use them for overnighters if needed. VTV also has a monthlies segment -- but also have a pretty large overnighters area. Including storage sites, they have over 1,000 sites altogether.
One of my pet peeves when I first started RVing was that the site I found myself in after registering had little resemblance to the site that was described to me on the phone when making the reservation. In Banning, CA, e.g., I asked for "NO TREES" due to my satellites. The site they sent me to upon arrival had more trees than any in the entire park. Had to go back to the office three times to get a site that would work for me. And the park was virtually empty at the time. That type of situation was the main reason my SW allows the operator to mouse click a site from the on screen park map to display a picture of the site for the RVer to see prior to leaving the office. However, if it's all done on the phone -- and you don't go through office registration when entering the park, that doesn't help.
As I work with different parks, it's interesting to note how the management of sites differs. On one end of the spectrum, a park will consider a reservation the holding of specific site until the RVer occupies it, or let's them know of a cancellation. On the other end are parks that will not assign a specific site to anyone until they arrive. They then make decisions on where to place that rig. I recall one park on the 5 freeway south of Sacramento that didn't assign a site at all -- just told me to park anywhere I found an opening. I asked it I should then tell them were I was located -- and they say, "No". Of course, there are tons of factors that lead to such decisions by owners and managers, or property managers.