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Driving along the Rio Salado Norte leads to another wonderfully exposed section of the Sifon Ignimbrite. Although this stop is along the main road, it is slightly inconvenient because just beyond the exposure cars are instructed to turn around due to land mines. The ignimbrite, however, is roughly 80 m thick in this part of the APVC.
The Sifon is crystal-rich, including large quartz crystals, plagioclase, biotite, hornblende, abundant pumice clasts and few lithics. The Sifon within the San Bartolo Group is a generally at is well to moderately indurated and has a fine-grained, crystal-rich (~65-70%) matrix.
The pumice rafts are not all connected throughout the outcrop, suggesting there may be a fault in the area resulting in differential flow movement between the blocks of flow.