The OP said:
I live in SW Fullerton
The first responder said:
The most direct route would be South on Glassell / Kramer to the River Trail
Ummm, not really. Not from
SW Fullerton, which isn't far from where I live in Anaheim (La Palma/Brookhurst). Usually, I drive to the RJ Noble quarry parking on Lincoln at SART/Batavia or to the Rampart access (Orangewood and 57, near the firetraining facility, south side of the stadium). Or I'll drive to Rynerson or Liberty Parks (Lakewood and Cerritos respectively) to ride SGRT. But lately I've been parking over at Maxwell Park in Anaheim (Haskett branch of the Anaheim Public Library, Broadway between Magnolia and Dale) and riding from there to either trail. And even up to the fairly new (and short, so far) Whittier Greenway. I even use Maxwell Park as a base for my every-couple-of-weeks trip to the Alamitos Bay farmers' market.
ETA: lotsa nice huge old trees to park under at Haskett if you get there early enough on the weekends to beat the soccer traffic