Hey mountain_rush, welcome to the forums. Don't know of any trails in LA area, I'm a bit far away. Think Disney WORLD, not Disney Land!
Regardless, you probably don't have a "Shimano" bike. It may have Shimano Components, but not a bike. What is the name on the downtube? Or, there may be a name on the headtube. If you post a picture of it, someone will be able to tell you what it is.
Anywho, welcome again!
L8R
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"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming, "WOW, What a Ride!" - unknown
"Your Bike Sucks" - Sky Yaeger