Selecting Map Points Inside a Map Poly

Question

I'm trying to find an algorithmic way to select which points fall within a specific arbitrarily shaped area on a Google Map. Basically I want to be able to provide a point and ask a function if that point lies within an arbitrary (but specifically defined) map area.

For example, how could I tell if a point was contained within the green section (Brions Regional Park) on the follow map:

http://maps.google.com/maps?ie=UTF8&q=state+park&fb=1&gl=us&ei=Rm-tTIGRBI2jnQeXrZyTBg&ved=0CEoQtgMwAw&sll=37.912242,-122.078705&sspn=0.086,0.17355&split=1&rq=1&ev=zi&radius=5.68&hq=state+park&hnear=&ll=37.934585,-122.13192&spn=0.089358,0.17355&z=13

I need help figuring out how to define the specific area and also then the algorithm that would take in the defined area & point and return true/false.

Thanks in advance for your help!