The Stanford Arboretum pre-dates the university. Leland Stanford began to plant it in 1880 and hoped one day to build a new residence to live in that would be surrounded by it. Instead, his son died unexpectedly in 1884 and the Stanford's instead decided to continue to live in their original house (a summer home; their main residence was located on Nob Hill in San Francisco) and to build a university in their son's memory. They remodeled the summer home in 1888.
Stanford purchased over 1200 trees and shrubs from a nursery in Flushing [in Queens County, on Long Island], New York, in late December 1879; it was the largest nursery purchase made thus far in the United States. The plants traveled to California via boxcar on the transcontinental railroad that had earned the Stanford's their sizable fortune.
Planting began in 1880 as the trees arrived. Chinese gardeners that worked for the Palo Alto estate planted them. Stanford learned the hard way that the hard clay soil did not allow for good root penetration. The Chinese used nitroglycerin to blast planting holes that enabled the transplanted trees to flourish.
Most of the trees, over 12,000 of them, were planted in 1884 under the direction of landscape gardener, Rudolph Ulrich, who also designed the Arizona Garden, which was located directly behind the site of the new residence. The Mausoleum was instead located at this site once the Stanford's decided to remodel their old house rather than build a new one.