The Sonoma-Marin commute rail agency is holding a ceremonial groundbreaking at the historic Petaluma depot Friday, attended by a large number of local, state and federal politicians to celebrate the beginning of construction.

Congress members Lynn Woolsey and Mike Thompson, state senators Mark Leno and Noreen Evans, Assembly members Jared Huffman, Wesley Chesbro and Michael Allen and Metropolitan Transportation Commissioner and? Rohnert Park Mayor Jake MacKenzie are scheduled speakers.

The depot is near where the Petaluma station platform will be built as part of the 38.8-mile line from Guerneville Road in Santa Rosa to downtown San Rafael.

SMART has awarded a $103 million contract to replace the rails and build the infrastructure for station platforms from Santa Rosa to the Marin Civic Center. The agency plans to award a contract for construction from the Marin Civic Center to downtown San Rafael in the next few months.

The contractors, Alameda-based Stacy and Witbeck Inc. and Herzog Contracting Corp., are preparing to start work this spring.

The groundbreaking is at 10:30 a.m. at the old Petaluma depot at Washington and Lakeville streets.