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We will probably always call it Silicon Valley. But the steady move of technology companies into downtown San Francisco is shifting the center of gravity of what is arguably America’s most innovative industry from the rambling, suburban streets of the Valley to the tightly concentrated and increasingly vertical neighborhood behind San Francisco’s Embarcadero.

Facebook’s decision last year to lease more than 400,000 square feet in a skyscraper across from the newly opened Salesforce Tower will put offices of the biggest names in tech — Google and LinkedIn among them — within walking distance of each other.

In the middle of all this is the Transbay Transit Center, which opens in June and is advertised as the Grand Central of the West.

“The building is starting to come to life,” said Dennis Turchon, senior construction manager for the Transbay Joint Powers Authority, the public organization charged with building the structure.