Hey Pickle,
Used to live there back in 00/01. There used to be this nice little area in River Legacy Park. I do not know if you are familiar with that park or not. It is on Green Oaks just east of Collins. Anyway, if you head down the paved path, you used to find MTB trails going off at several places. I understand that now they have MTB dedicated trails, but I have not been there since 00/01. The only other thing I would suggest is go into the local shops and ask. I got hooked up here in Houston just by asking, it is also a great way to find fellow riders.