Milestones

Ten years ago: President Reagan and Canadian Prime Minister Brian Mulroney signed an agreement to lift trade restrictions between their countries. An Ashland Oil Company tank collapsed in West Elizabeth, Penn., sending more than 700,000 gallons of diesel oil into the Monongahela River.

Five years ago: President Bush arrived in Moscow to sign a strategic arms treaty with Russian President Boris Yeltsin, who hailed the agreement as “our joint gift to the people of the Earth.”

One year ago: Rain and melting snow swamped the West, trapping visitors in Yosemite National Park, closing casinos in Reno, Nev., and forcing the evacuation of 50,000 Californians.