Is there a geologist in the house?

My brother and I took an interesting little ride up Sulphur Creek. From Market St. we went in through Satan's Tunnel (some sweet graffiti) along the creek which takes you in a Northwest direction, in the canyon between Quartz Hill Rd. and Lake Blvd. About a mile in, we came to a place where some trail building and brush clearing has taken place. We saw official looking markers that said, TRAIL. Although it is short, we rode it absolutely delighted, due in part to the perfect traction the previous nights rain had created. I have always been a bit of an amateur geologist/archaeologist and am always on the look out for features that might reveal fossils. So when the trail dropped down to the creek and I saw the stream bed running over limestone, I told Tim to stop so we could have a look around. Proceeding up the Creek on foot, I came to a place where the stream bed appears to be lined with some kind of man made aggregate, but I think it's a natural geological occurrence. This beautiful little recreation area is a jewel right in our fair city. Even though I used to ride through there (15 years ago) on a regular basis, I am going to rediscover what is out there. Want to go?