70% fireroads and some nice singletrack here and there if you know where to look. These trails are burly and not for the faint of heart, but are absolutely the BEST for training or making everything else you ride seem easy. Its made up of super steep hills that- once you've made it to the top- wrap around the ridge that is the western border of lafayette. The views are pretty spectacular. depending on where you are, you can see anywhere from the carquinez straight, to mt. diablo, to Danville/Orinda/Moraga. It's mostly grassy oak woodland, and gorgeous in spring especially. Lots of people give up before they reach the top because of the steep ascents, but hey, you're up quick- 25 mins or so- and if you use the short breaks on each climb wisely, you'll find them broken up nicely for quick breathers (it's even faster if you cut up Martino Rd on the pavement at a 20% grade... ten minutes of pain and you're 3/4 of the way then it's 10 mins of dirt to see the entire ridge from the top). The ridge forms a large "C" that you'll be able to see arching west, then north, then back east, roller coastering up and down as it drops back down to the top of springhill rd. There were lots of climbs on this trail that initially, I thought were impossible (and I've been riding my whole life). Now, 7 years later, I can say I've made all but one, and even that one (the dreaded "double hump") I've seen buddies do. This place is tough, and there are definitely more fun places if you're looking for jumps, berms and a ton of singletrack, but it's my home ride and I love it. Everything else i ride, all season long, is cake, and I have Briones to thank for that.