The UW Continuing Education Department offers this history of the trees:
"30 Yoshino cherry trees are the hallmark of the University of Washington Quad. They were first planted on land that is now the approach to SR 520, but were relocated to campus during construction of the bridge. Estimated to live between 60 and 100 years, the trees are approximately 63-73 years old. In anticipation of replacing them, the UW Class of 1959 launched the Cherry Tree Project. Cuttings were grafted onto rootstock, and replacement trees are growing in a nursery in Mount Vernon, WA. Visit the original cherry blossoms in the Quad as they begin to bloom now through April. And keep learning. It's the Washington Way. http://www.keeplearning.uw.edu"