I love this trail (or network of trails), and ride it 2-3 times per week. It truly has something for everyone: I take my 5 yr old son with me by trailer-bike on the main cowiche canyon trail (which is a great ride except for some places of deep gravel). Then there are the upper loops accessed from the scenic drive parking lot for more of a challenge / workout, and finally there is the more technically challenging descents and snake coil. One trail I don't see on the map is the winery / vineyard trail that originates off of the main canyon trail just west of where the uplands trail connects. It goes up the other side of the canyon and is very steep (mostly off my bike on the way up), but the descent back down is rocky steep and challenging (at least for me).
I'm still finding my way around and it's true that the trails are not well marked - but it's a lot of fun and a great ride. There are dogs and hikers - and also watch out for snakes (I have seen them right near the trail 3 or 4 times). I'll post some pictures.