New California city backed by Silicon Valley billionaires will be about 18,600 acres — less than half the size of the purchased land

• The company backed by Silicon Valley's elite unveiled more details behind its new California city.
• The plans propose "one of the most walkable" cities in the US with a total size of about 18,600 acres.
• That still leaves about 36,000 acres the company purchased from landowners throughout the county.

More details on the elusive new California city that is backed by some of Silicon Valley's wealthiest were unveiled Wednesday as the company spearheading the project prepares to put its ambitious plans on a ballot initiative and gather local support.