Drains poorly. There are often huge sections underwater for most of winter and spring, stranding sections of trail. It also sees heavy equestrian use so the tread is often soft and rutted. There are couple fun sections that offer a small technical challenge and roll around the small hills on the property.
http://your.kingcounty.gov/dnrp/library/2006/KCR1951/figure8-roads-trails-access-map.pdf http://trails.evergreenmtb.org/wiki/Trail:Island_Center_Forest_(Vashon_DNR)
There is a parking lot and trailhead off of SW Cemetery Rd on 115th Ave SW. Parking is very limited on 115th Ave SW off of SW Bank Rd. You can access the trails just north of the transfer station on Westside Highway. Parking for horse trailers can be found at SW 188th St and 107th Ave SW.
http://www.singletracks.com/item.php?c=1&i=7073