La Mina de Tarta
					Caution: this circuit passes near la Mina de Tarta, an active calcite mine. This activity is noticed by many a visitor to the Potrero as dynamite explosions that rock the canyon - wake-up call on many a morning. For your own safety avoid running this loop during weekdays: wait until just before sunset, go at night with lights, or go on a Sunday when the mine is inactive. At these times it is also possible to check out the mine (at your own risk!); there are interesting large calcite crystals to be found.
	Description. Begin at Rancho Cerro Gordo and follow the usual exit route to the paved road. Or, for extra variety, after you pass the casita, take a right onto a small rocky track and follow it with some difficulty until it T's; turn left and descend into the arroyo (stream bed) to rejoin the main RCG driveway. Once on the paved road turn right towards the Potrero but take the next right onto a dirt road which re-crosses the arroyo. The uphill grind begins here. See how fast you can climb without blowing your top (we can usually make it in 8 minutes). At the top of the hill you will be rewarded with a great view of the Popa, Cerro Tia Chena, the towns of Mina and Hidalgo (splendidly lit up at night), and the Potrero Grande. If you wish continue uphill to check out the mine, or take a right onto an old, forgotten mine track. Traverse the hillside in several rapid swoops, then fork right at a difficult-to-find, overgrown trail. You will cross three technical bulges before the trail widens into a 2-track. If the road turns left and begins to climb again, you've gone too far. Careen down the gravelly 2-track past several gentle yet treacherous curves, until you arrive at a well-defined fork. Go right, and continue your fast descent over gravel and rock jumps. The road turns right and descends steeply and loosely into an arroyo. An unexpected steep uphill follows, with a gate on top. Hop the gate and continue on the old road until it turns left and downhill; make a sharp right here onto a small singletrack (a bit difficult to find). The singletrack sports four technical obstacles: an arroyo crossing, a rocky uphill, a downhill with a rock step, and a difficult uphill on rough bedrock, in that order. As you crest the top after the first hill, go left of the fencepost and bear slightly left to stay on the trail. After the crux uphill you will be on a wide doubletrack, and the rest of the ride is easy. Follow the road in the direction of the water tower, passing an old dump to your left. Take the 2nd right after the dump, again toward the tower. The road twists right and descends to cross an arroyo; you can do a little stunt here by veering right onto a small track, then dropping down a steep embankment back onto the road. After climbing out of the arroyo take a right and head uphill. Try to ignore the neighborhood dogs as they try to intimidate you (Mexican dogs rarely bite - they know what they've got coming to them if they do). Passing rancho land, the road eventually T's; go right. Three lefts around the block will take you back to Rancho Cerro Gordo. This is a brisk ride which can be done in 30 minutes or so, if you don't lose the way.