MOUNTAIN VIEW -- Google has quietly spent $600 million over the past several years in a real estate shopping spree centered on this quiet suburban Silicon Valley city that already houses its corporate headquarters -- one that could pay off with huge new expansion opportunities for the Internet giant and reshape the community's skyline.
Starting in 2011, Google has bought about 24 office buildings in Mountain View, most of them nondescript and low-slung.
But if city officials change zoning rules in northern Mountain View, the existing buildings likely would be transformed into much taller, much sleeker spaces that would give Google room to house the thousands of workers the tech titan is hiring in close proximity to the Googleplex, the nickname for the company's headquarters on Amphitheater Parkway.
The city says it will issue a final decision by year's end. After that, property owners would have to submit specific proposals.
The stakes for all this are considerable. Mountain View feels pressure to allow higher densities for offices to continue to grow as a city. Some residents are alarmed enough about growth that they make seek a referendum on one or more proposals and are making this year's City Council elections a barometer on growth issues.
Google won't say if it will seek approval for big buildings on the sites it is buying. However, commercial real estate industry experts say the company is focusing its purchases in areas where the city is considering high-density development that would yield taller offices, expected to be five to 10 stories high.
And were Google able to redevelop just 20 of its sites with modern offices of 100,000 square feet each, that would be 2 million square feet of new space with room for 10,000 employees. That would be one-fourth of the estimated 39,000 people who work in downtown San Jose.
Mountain View is the hub of an extraordinary burst of real estate activity by Google, which is busy buying or leasing sites in a swath that stretches about 10 miles along Highway 101 and encompasses three cities.
At the northern edge of this stretch is a cluster of nine Palo Alto office buildings. Then come two more clusters of buildings close to the Googleplex. Also near the Googleplex is a proposed 1 million-square-foot campus at NASA Ames. Adjacent is Moffett Field, where Google will preserve and redevelop Hangar One and other facilities. At the southern terminus are several big office buildings Google leased in Sunnyvale.
The tech titan says it wants sites that form natural clusters.
"Google is a growing company, and our real estate needs are re-evaluated on an ongoing basis to make sure we're ready for what the future holds," said Meghan Casserly, a Google spokeswoman. "That's why we often look for proximity. When multiple pieces of property become available nearby, it's helpful to accommodate for natural growth."
The possibility of high-density office spaces in Mountain View -- and the resulting traffic -- have alarmed some community leaders, including Lenny Siegel, executive director of the Center for Public Environmental Oversight.
"The projected growth in employment is tens of thousands of people, and the anticipated growth in residential construction is on the order of thousands of units," Siegel said. Expensive housing and clogged streets will result, he warned.
If the city doesn't meet their wishes for balance in new jobs, homes and traffic, the Campaign for a Balanced Mountain View, a group that includes Siegel, said it may pursue a referendum to reverse the looser development rules.
What's more, a City Council election is scheduled for November, keeping the issue on the front burner.
Google has previously collected offices in Mountain View. In 2007, the company grabbed space up and down Shorebird Way. Now, Google signs and workers riding colorful Google bikes dominate the street.
When Google launched the current buying binge in 2011, observers were puzzled. The decades-old structures didn't fit the mold of the modern offices Google was leasing. Yet seen in the context of Mountain View's lack of sites for large new office buildings, the purchases leave Google poised for a major expansion of its operations, depending on the city's density decision.
"Mountain View is running out of land," said Phil Mahoney, an executive vice president with Cornish & Carey, a realty firm.
Some analysts argue that Mountain View must increase density or be hobbled by feeble growth.
"We want to ensure that Mountain View retains its economic vitality, that it remains a place where businesses and people can still grow and locate," said Randy Tsuda, city community development director.
In 2012, Google used a letter about Mountain View's general plan to publicly back the concept of higher densities, coupled with smart transportation.
Transportation efficiency and land use are "inextricably linked," David Radcliffe, Google vice president for real estate and workplace services, wrote in a letter to city officials.
"The office park development model has played itself out," he wrote. Sprawling business parks in north Mountain View would yield to higher-density offices, more housing and an improved transportation system that would serve the taller buildings and additional workers, Google said in supporting the city's general plan.
Google's quest for space has caught the eye of developers who are betting on a boom in Mountain View underpinned by robust rents.
"It's like you're developing on Boardwalk or Park Place," said David Vanoncini, a managing partner with Kidder Mathews, a commercial realty firm.
Sobrato is building a big office building in Mountain View on parcels the developer collected, said Chase Lyman, Sobrato's director of commercial real estate.
Experts think Google is in good shape for expansion, despite the tech industry's boom and bust cycles.
"Technology does ebb and flow, you had Atari and Worlds of Wonder, and we've seen Apple go from boom to bust to boom again," said Jim Beeger, a senior vice president with Colliers International, a commercial realty firm. "Google has been different. The most they do is take their foot off the accelerator a bit. We've never seen Google hit the brakes."