SAN FRANCISCO (CBS SF) — San Francisco’s iconic red-and-white Sutro Tower is celebrating 40 years of transmitting broadcast signals throughout the Bay Area.

The 977-foot-tall steel tower, which holds about 200 antennae, was completed in 1973 after a $4 million construction project that started in 1971. The tower began transmitting signals on July 4 of that year.

READ MORE: Big Sur Residents Told to Boil Water Due to Possible Wildfire Damage to Utility

Workers, engineers and neighbors of the tower planned to join city leaders at the festivities today, which were slated to include a barbecue and cake.

Tower spokesman Dave Hyams said former Mayor Willie Brown and Supervisor Norman Yee were in attendance.

The tower, named for the hill, Mount Sutro, from which it rises, is used by 11 television stations, four FM radio stations, satellite and cable providers, and public safety agencies and commercial wireless communication services.

Hyams said there is no danger of the tower becoming obsolete, even as fewer Bay Area residents receive over-the-air TV reception.

READ MORE: Hazardous Sneaker Waves Threaten San Francisco Beachcombers

“As wireless technology grows, there’s more need than ever,” he said.

The tower was built as residents of the growing Bay Area were struggling to receive quality TV signals from existing towers, Hyams said. Weak signals were a problem in some parts of San Francisco and in the outlying suburbs, he said.

Hyams said the tower has changed very little since it was erected.

He said everything is checked and maintained throughout the year, and that the biggest challenge is the fog. Repair crews are constantly battling the moisture that causes corrosion and rust, Hyams said.

The 40th birthday party began at noon at 1 La Avanzada St.

MORE NEWS: UPDATE: Air Attack, Calming Winds Aid Firefighters Battling Wildfire Near Big Sur; Containment Grows To 25 Percent

The tower is not open to the public and is operated by Sutro Tower Inc., a corporation founded by owners of several local TV stations.