One of the last remnants of the Telecom Valley cluster of high-technology startups that at once employed several thousand in Marin and Sonoma counties has relocated its headquarters to Silicon Valley.

Calix Inc. (NYSE: CALX) is shifting about 125 Petaluma employees from 82,000 square feet of offices at 1039 N. McDowell Blvd. to the entire 22,000-square-foot second floor of 1435 N. McDowell. That’s expected to be completed in February. Meanwhile, Calix opened a 65,000-square-foot new headquarters office in San Jose, with room for over 300 employees.

Calix said in the past five years the company has transformed from being just an developer of equipment that connects telecommunications companies to broadband networks to a creator and manager of cloud-based communications platforms.

Being based in Telecom Valley “helped Calix establish a leading position in the broadband access market,” said Carl Russo, president and CEO, in the headquarters announcement in September. “Now as a communications platform provider our mission is to connect everyone and everything.”

And that modern connectivity is also partly behind the downsizing of the Petaluma footprint, a spokesman told the Business Journal.

“As we’ve grown, our teams have spread out, and we have more people working remotely and in completely different geographies — many far from the Bay Area,” said Dale Legaspi of Calix.

Calix was co-founded in 1999 by Mike Hatfield, just after the eye-popping nearly $7 billion deal sale of another Petaluma telcom startup he had a hand in creating, Cerent Corporation. That deal put Telecom Valley on the global map of telecommunications equipment development. Hatfield went on to co-found yet another Petaluma telcom, Cyan, which was sold to Cienna in 2015 for $400 million and still maintains a high-profile development center in the city.

The current president and CEO of Calix, Russo, also is a Cerent alum, running that company before the Cisco sale and in a top role at that Silicon Valley company for a few years afterward. He was on the board of Calix before stepping up to the helm in 2002.

Calix hacquired Optical Solutions of Minneapolis in 2006, Santa Barbara-based rival Occam Networks in 2011 and the fiber-optic network access assets of Ericsson in 2012.

Revenues for the first three quarters of 2018 were $325.8 million, down 12.5 percent from a year before. Revenue for the fourth quarter, to be reported Feb. 5, was forecast to be $122 million to $127 million.

In the August lease deal for Calix’s new Petaluma offices, Whitney Strotz of Cushman & Wakefield represented Calix, and building owner Cornerstone Properties handled its own side.

Jeff Quackenbush covers wine, construction and real estate. Contact him at jquackenbush@busjrnl.com or 707-521-4256.