[FREE HARDCORE] The striking white stallion that adorns the cover of Zero Hour probably wasn't meant as a sight gag, but it works as one: Palo Verde, you see, is no one-trick pony.

Drummer Lauren K. Newman and guitarist Terrica Kleinknecht are, however, a group with a shtick: All of the duo's material is strictly instrumental and improvised. This is as true in the studio—where Palo Verde is confident enough to record to expensive analog tape—as it is in concert.

At the outset, I wondered how much the band's second album could differ from its first (History for the Rest of Eternity, released in 2010). After all, the only embellishments on Palo Verde's songs—which range from seven to 15 minutes on Zero Hour—are feedback and simple effects-pedal sounds captured live. But the lack of predetermined structure doesn't equate to formlessness: Kleinknecht and Newman seem more mindful of this on Zero Hour than they were on History. 

Improvised doesn't mean themeless, either. The album's apocalyptic message (white horse, get it?) comes across well before the two-minute speech on corporate power from activist/radio host Alex Jones. Kleinknecht, who seems to take the lead more often than not, plucks stray notes from "The Star-Spangled Banner" on sprawling opener "Dark Meadow For Long Night." "Evening Shadow" opens all metal before bursting apart and spilling its guts in every direction.

It's best for everyone that Palo Verde limits itself to four songs here: Even in its truncated form, Zero Hour clocks in at 44 minutes and is likely to test the patience of all but the most committed guitar-tone enthusiast. But in that 44 minutes, the joy of anticipating Palo Verde's next move, only to often be proven dead wrong, should hold as much appeal for bebop lovers as it does for metalheads. To great artists, strict creative parameters present opportunities. Palo Verde is going to ride this horse as far as it will take the band.

SEE IT: Palo Verde plays Record Room, 8 NE Killingsworth St., on Sunday, May 13, with Fucking Lesbian Bitches and Older Women (yes, those are band names). 8 pm. Cover. 21+.