Prosser pits as they are called are not a destination mx track IMHO. But, there are tons of trails around there to launch to that make it a worthwhile spot to park and ride for a bit before exploring the surrounding areas. Prosser Hill (the animal), trails and dirt roads out to Boca and Stampede, etc. Tons of fun stuff scattered all over those woods.
full disclosure: I am not an MX rider, I like woods and trails.