MOUNTAIN VIEW — In a head-spinning mega-deal, Google has paid $1 billion for a huge Mountain View business park, the Bay Area’s largest real estate purchase this year.

It is also the second-largest property purchase in the United States this year, eclipsed only by another Google acquisition, the $2.4 billion the company paid for Chelsea Market in Manhattan.

The newly acquired site in Mountain View, where Google has been the primary tenant, is larger than the property that accommodates the company’s Googleplex headquarters a few blocks to the west and also exceeds the size of the parcel across the street where Google is building an iconic “dome” campus that features canopies and tents.

“Wow. What a deal,” said Chad Leiker, a first vice president with Kidder Mathews, a commercial real estate firm. “This is an opportunity for Google to own more office space very close to their headquarters. That office space is becoming very rare in Mountain View.”

Google’s Mountain View purchase means that in the two years since the search giant began to collect properties in downtown San Jose for a proposed transit village, the company has spent at least $2.83 billion in property acquisitions in Mountain View, Sunnyvale, downtown San Jose and north San Jose alone.

Adding to the eye-popping numbers: Google’s spending activity in those four markets reaches $3 billion when including the company’s pending purchase in downtown San Jose of several government-owned parcels, along with the minimum value of a big set of surface parking lots that Google intends to buy from Trammell Crow, also downtown near its proposed transit village.

Buying Mountain View’s Shoreline Technology Park gives Google a 51.8-acre site with 12 buildings. The big parcel, which is dominated by one and two-story buildings with ample surface parking, has addresses ranging from 2011 to 2091 Stierlin Court. Aside from Google, a survey of the site indicates that the only other tenant in the complex besides Google is Alexza Pharmaceuticals.

“This is in Google’s core campus area, and they would certainly want to own it and control it rather than continue to lease it,” said Philip Mahoney, executive vice chairman with Newmark Knight Frank, a commercial real estate firm.

“The property begs for redevelopment with higher densities,” Mahoney said. “But that would be a much longer discussion and process” in connection with Mountain View’s development plan for the areas north of U.S. 101.

Since its December 2016 purchase nearly two years ago of an old Pacific Bell building near the Diridon Station in San Jose, Google, directly or through affiliates, has spent at least $1.32 billion buying sites in Sunnyvale, $1 billion acquiring properties in Mountain View, $271.8 million in north San Jose and $234 million obtaining parcels in downtown San Jose.

Google’s agreement to pay $109.9 million for government-owned properties in downtown San Jose, as well as the minimum value of $58.5 million for a nearby Trammell Crow-owned site, brings the company’s buying surge in those four markets to $3 billion.

A Google representative confirmed the $1 billion purchase price for the office park but didn’t comment beyond that.

Irvine-based HCP, a realty investment firm, sold Google the Mountain View property on Nov. 20, Santa Clara County records show. HCP stated in a regulatory filing that it realized a $700 million gain from the sale. The property’s assessed value in mid-2018 was $367.3 million.

“This latest deal in Mountain View could be a case, as they have done in other areas, of Google land-banking properties for higher-density uses later,” Leiker said. “They have bought a huge tranche of properties.”

The deal also appears to be the Bay Area’s largest real estate transaction — by far — in 2018. Prior to Google’s purchase, the highest price paid in Silicon Valley was a $284 million acquisition by developer Jay Paul of the Cityview Plaza office, retail and restaurant complex in downtown San Jose in July. That was topped by the October deal for San Francisco’s iconic Ferry Building complex, a $291 million transaction.