Don Gaspar de Portola
From Palo Alto Wiki
Don Gaspar de Portola led the first white party into the Palo Alto area. They emerged from the San Andreas Canyon on Nov. 6, 1769 and followed the San Francisquito Creek toward Palo Alto. It was an accidental find, as they had been searching for Monterey Bay.
Historians debate whether Portola camped under the twin trunks of El Palo Alto (where the Native Sons and Daughters of the Golden West placed a plaque in 1926) or if they camped on the north side of the creek near Alma Street in Menlo Park (where the state Historical Landmarks Committee set up its plaque). At any rate, Portola left his camp on Nov. 11 and headed back up the canyon after envoys found no clear route through the East Bay, a phenomenon that exists to this day.
Historians also cast doubt about the authenticity of El Palo Alto, it is generally accepted that a portion of that famous tree still stands next to the railroad bridge near Palo Alto Avenue and Alma Street.
It is said that the men in the Portola expedition gave the name to the 35,250 acre Rancho de las Pulgas. In 1769, while the party was camped near the mouth of Purissima Creek. Some soldiers reportedly decided to leave the camp and sleep in deserted Indian huts on the north bank. But they fled from the huts before the night was over, crying "las pulgas!", or "the fleas!". Portola's army engineer used the name to identify the Indian village and it stuck.