Listening to a Littlest Birds album is like walking into an antique shop and gradually realizing something is amiss: The elegant pieces of furniture are so unmarred they might be new; they even smell that way. The pages of the period calendar on the wall aren't yellowed. Despite the decades-old date, it's apparently new as well. Then when you look out at the street scene through the showroom glass, the 2013 cars you just left have been replaced by a mix of Packards, Buicks, and Aston-Martins from the 1930s.

One possible reason for the musical duo's time-travel illusion is the Birds' unusual, and minimal, pairing of instruments. "There aren't a ton of banjo-and-cello arrangements out there," says cellist David Huebner. "It's a unique sound that caught us by surprise. It's a really full sound, to be just a pair of instruments.

"We started just playing casually, and strangers would come up and compliment us on the sound, like 'That's really cool!', and we'd be like, 'Thanks, but we're just having fun, here.' We didn't know." Nowadays they've evolved to playing for appreciative strangers in much larger groups, such as their Saturday-opener concert at Beartrap this weekend.

The other Littlest Bird is banjoist Sharon Martinson. The two hail fromMammoth Lakes,California, but currently call the town ofBishop, in the eastern Sierras, their home base. ("Start inSan Franciscoand drive exactly 600 miles east through the mountains and you're there," Martinson says.) The fact that their cello and banjos (multiple: open back, clawhammer, nylon and steel, et al) look so well- and duly-worn that they might have been around in Great Depression days doesn't hurt the anachronistic effect either.

It's rumored that their name comes from the title of a song popularized by theAmericanagroup The Be Good Tanyas. Its chorus explains, "The littlest birds / Sing the prettiest songs..." "And Dave and I are both the smallest people in our respective families," Martinson tells an interviewer. "So, there's that."

The concept of home is an especially welcome one these days for Martinson and Huebner, who in the spring and summer of 2012 completed a 53-show tour that involved 15,000 miles of driving. "This year we're actually looking forward to having a home and coming back to it," Huebner says.

The emotional territory covered by the Littlest Birds' lyrics will be familiar to lovers of "O, Brother Where Art Thou," Gillian Welch, and The Civil Wars. But there are occasional touches of humor that spring surprisingly from the gothic landscape, as in a song they co-wrote called "Rain on the Roof": "I hear rain on the roof / Like popcorn in a pan / It’s cold as a witch’s gap tooth / And I know it’s winter all over again..."

Martinson's and Huebner's musical backgrounds are only slightly more different than daylight and dark. Huebner was "born and raised playing classical cello," as he puts it. "Orchestras and competitions all the time. Then I gave it all up for a while, but eventually started writing some songs and picked up the guitar. I decided that music is really what I want to do, and it's been growing ever since--a several-year process, being in different bands, trying to get out on the road and get some exposure."

Martinson, meanwhile, started her musical road with the classical French horn that she played throughout college and grad school. But her career interest was in being a research scientist, which is how she came by her Ph.D. in Ecology and a one-on-one relationship with bark beetles and other species. It's the Ph.D. that she credits, or blames, for her addiction to banjo:

"My grandfather had given me his banjo to take out to grad school and keep me company. In the fifth year, when I was having to crank out my dissertation and was coming up with every possible procrastination tool, like cleaning the toilet twice, I said to myself, 'I should learn to play that banjo!'"

She met Dave when one of her biological field study sites in the Sierras happened to abut the driveway to his house, and one evening when she was leaving work he was sitting on his porch playing cello.

In the small-world department, one of the Littlest Birds' songs owes its pedigree to a visit Huebner made in 2010 toCasper'sNationalHistoricTrailsInterpretiveCenter. Its title is "Western Trail," and it's also a fair summation of their musical endeavors these days: "We've got one foot in tomorrow / One foot in yesterday / We've got one step still before us / Give us hope and give us strength..."