Mt. Diablo High School has been at its present site since 1905 when the first building was built on the land Mr. George Maltby donated, which extended from Grant Street on the west to East Street on the east, and from the alley by the shops north to High School Street.According to "Mt. Diablo High School A History", which was published in 1985, the land "was in the center of a large field studded with giant oak trees."
The oldest part of the shop building has been torn down and will be rebuilt to bring it up to code. Old portables have been torn down and new ones have been put up in the quad and in the student parking lot by the tennis courts. New buildings (dance studio and weight room) have been put up by the gym, and new buildings are under construction where the old portables used to be.Where there is new paving throughout the entire school, all of the trees and old benches between the Commercial and Academic Buildings have been taken out. New cement seating areas have taken their place.