On the climb to Oyacachi (and unfortunately, we didn't make it all the way, we just got to the crest of the main ridge before you start descending 900 M vertical to Oyacachi), it's all hardpacked gravel, nice and gradual climb, after you leave the cobblestone section. We climbed 14 km to the top of the ridge, through some awesomely barren scenery. Try and pick a clear day - we didn't, and froze the whole way. On the way back down, take the main road until you get to the cobblestone section again. Go left on the cobblestones (the way you climbed) until you get to a road going off to your left again, dirt. Climb that for about 500 M (to get away from the bogus cobblestones, which suck for descending), then turn right. Pick your way across the ridge, occasionally climbing a bit, to avoid any other cobblestone roads going to Cangahua. Eventually you'll hit a good sized spread among all the little ones; follow the canal along the top of that for a bit, then start heading down the hill; find the stream and cut along the bottom of it until it's not rideable, walk down the rocky section, then cut to your left a bit to hit another road. On that one, go down about 100 M until it opens up again to your right (downhill), and follow that road back to the main cobblestone road you initially climbed. Email me if you want more details, email@example.com. The downhill after the first cobblestone bit is a great mix of singletrack, gravel and everything in between.
Driving north from Quito, take the main road to Cayambe. About 7 km south of Cayambe, just a km or less from the little ball that is to the left of the road (going north) marking the equator, is a paved road to the East (right). It is marked as the entrance to Hacienda Guachalá, and prominently signed. Turn onto this road, and drive up about 5 km until you get to Cangahua, where you will drive into a little plaza. There is a road on the far side of the plaza that goes to your right, then turns left to head up the hill - this is the road to Oyacachi. Anyone in town can help you with that. In front of the church in the plaza should be a number of pickup trucks that do 'viajes'. Leave your vehicle in the plaza, and hire one of these to take you up the road as far as the end of the cobblestones, should cost you about 10 bucks, and take about 20 minutes.