Michael Schall's pencil drawings are perfect specimens of nature perverted. They are so meticulously executed that they're almost threateningly credible, and the rest of their quiet menace comes from the fact that their outré scenes are familiar. The day I saw Schall's eight-foot drawing of cruise liners and cargo ships locked in battle in a sea of cracked glacier fragments, I saw a news photo of the same thing. The series is called Firefall after the old nightly summertime ritual of Yosemite park rangers: They'd throw burning embers off a 1,700-foot cliff at Glacier Point. Tourists loved it. It lasted almost a century, then it was outlawed: It was "not a natural event." (Platform Gallery, 114 Third Ave S, 323-2808. 11 am–5:30 pm, free. Through March 27.)