The Bolsa Chica Wetlands is a great place to run. This 1200 acre nature preserve is in Huntington Beach w/ parking on PCH accross from the life guard station or at the corner of PCH and Warner Ave.
I try to run in there once a week. I'd guess there are about 10 miles of single track and dirt road throughout the preserve, and it's pretty easy to put together 4, 6 & 8 mile loops from either parking lot.
It's a local go to place for wild-life photography, plus if your a military history buff, there was a WW II coastal battery there, so the gun turret foundations are still in there.
Plus I find that basically every run I do in there is 110% relaxing and fulfilling.
Check it out:
If anyone is in the area and wants to go for a run, let me know.