In a stunning $3.5 billion deal, Blackstone Group LP is selling its Silicon Valley portfolio — a mammoth 8.2 million square feet managed under the Equity Office Properties flag — to Hudson Pacific Properties, a Los Angeles-based real estate investment trust, the Wall Street Journal reported Sunday night.

The deal, which is not yet closed, marks the end of an era in Bay Area real estate. Through a series of mergers and acquisitions, Equity Office grew to become a dominant player in the region’s office market. And while Blackstone in recent years has been selling off the EOP portfolio in dribs and drabs, it remained a massive owner of office buildings here. Its holdings include prime assets in some of the best locations — such as Palo Alto, Menlo Park and Redwood Shores.

The Journal said Hudson Pacific would pay $1.75 billion in cash and the rest in stock. The deal will give Blackstone a 48 percent ownership stake in Hudson Pacific, meaning that the company still has an interest in the performance of the region’s office market. The price would work out to $426 per square foot.

Eastdil Secured represented Hudson Pacific, while Goldman Sachs represented Blackstone. The companies weren’t immediately available to comment late Sunday.

On an earnings call on Monday, Hudson Pacific executives said the initial capitalization rate, a measure of yield, would be 5.1 percent. But that number is expected to rise above 7 percent after stabilization.

Hudson owns seven buildings in San Francisco but nothing in Silicon Valley, according to its website. The company, whose market cap was $1.88 billion as of Friday, currently owns 27 properties totaling about 6.4 million square feet in Los Angeles, San Francisco and the Pacific Northwest.

The buildings that will trade include some high-profile gems. Among them: Palo Alto Square at 3000 El Camino, 2180 Sand Hill on Menlo Park’s “venture capital miracle mile” and several projects in Redwood Shores, including the Towers at Shores Center and 555 Twin Dolphin Drive. It is also the dominant owner in the San Jose airport submarket.

I’m told that the deal does not include Equity Office’s San Francisco assets — the Ferry Building in San Francisco or 100 Montgomery St. The deal also does not include 10 Almaden, the downtown San Jose office tower that sold to KBS REIT III this month.