The Mollys first attracted attention for their unusual hybrid sound -- a mix of Irish folk songs and Tex-Mex corridos cemented together by an accordion and driven forward by an energetic roots-rock rhythm section. The Tucson quintet's sixth album, "Moon Over the Interstate," however, is most notable for the power of Nancy McCallion's songwriting. She rivals Lucinda Williams and Iris DeMent as one of the finest Americana songwriters of the '90s and she deserves a comparable reputation.

McCallion puts the Molly's Tex-Mex influences to good use on "The Sierra Madre," a first-person tale of a Mexican peasant embittered by economic forces that declare "poppies are worth more than cornmeal, dollars are worth more than life." McCallion hands off the lead vocal to the band's co-leader, Catherine Zavala, whose throaty alto catches the song's blend of resentment and stoicism. Zavala also sings "The Lang Town," a very funny narrative about Scottish miners who went on strike over their supply of whiskey.

That song showcases the Mollys' lively Celtic sound. The same sound frames McCallion's vocal on "Rosie," a sharply etched portrait of a woman on an Arizona reservation. The Irish and Mexican influences come together on the title track, a child's-eye view of a single mother flying down the highway from one more ex-lover and one more landlord.

Appearing Friday at Paddy Mac's. n To hear a free Sound Bite from the Mollys, call Post-Haste at 202/334-9000 and press 8120. (Prince William residents, call 690-4110.)