What's new is old at Twitter's new San Francisco headquarters.

The high-tech firm has a new look for its old logo, a new office in an old building and, in a few weeks, new dining rooms in some very old log cabins.

In keeping with the designer's forest-themed interior motif, a pair of homesteader cabins from the late 1800s are being installed in Twitter's new digs in the historic Western Furniture Exchange and Merchandise Mart building, a 1937 art deco landmark on Market Street.

In a few weeks, Twitter employees will be able to eat and hang out inside these Old West relics, which still bear the adz marks of the ranchers who built them 100 years ago.

"You can see the hand of the original craftsmen who built them," said Olle Lundberg of Lundberg Design, the San Francisco architectural firm responsible for the specialty design elements in the new office. "It's kind of cool that cabins that were built sometime in the 1800s have now reappeared. The guys who built them are long dead, of course, but are sort of still here. I kind of like that."

Lundberg bought the cabins for an undisclosed price after seeing an ad on Craigslist placed by Novato contractor Karl Beckmann, who salvaged them from a couple of remote ranches in small Montana towns.

"We advertised them for a year and we pretty much got a lot of crackpot calls," Beckmann said. "When you think about it, buying a 100-year-old log cabin that has been exposed to the elements is not a very practical idea unless you're doing something exactly like what is being done here."

Lundberg, who lives in a decommissioned Icelandic car ferry docked at Pier 54 in San Francisco's Mission Bay, had already reused wooden planks from the lanes of an old bowling alley, with some of the original nails still visible, to build the reception desk in Twitter's main lobby, which features real tree branches sandwiched between layers of glass. As wall decor, blue Twitter bird logos have been fashioned out of vintage California license plates, and # and @ symbols have been routed into slabs of raw wood.

In this spirit of reuse and reclamation, Lundberg saw the cabins as a novel way of breaking up the wide open spaces of a gutted floor in the old furniture mart that will become a casual dining area. The 20-by-20-foot cabins serve as rooms within a room, adding intimacy to the impersonal space. And the fact that they're built of old lodge pole pine logs fit into his overall woodsy design scheme.

"We've used the notion of the forest as a nice tie-in with Twitter and its bird logo," he explained. "To me, the log cabins fit into that since, obviously, they're made from logs that come from the forest. It's also about using natural materials. There's something nice about the character of the real wood. Visually there's a patina of age. It isn't something fake. It's real. It's reclaimed. It's got some history to it, just as the building has history to it. One of the nice things about reusing old materials it that there is a story that comes with them."

Beckmann, owner of Beckmann Engineering and Design and Beckmann Construction in Novato, had the cabins taken apart in Montana and shipped to a company yard in Vallejo, where they were put back together. The cabins were then taken apart again and trucked to Twitter's new office on three floors of 1355 Market St.