One of the largest picnics in the nation will take place Saturday, April 22, when tens of thousands of people come to the University of California, Davis, for its annual Picnic Day. Opening ceremonies for the daylong 82nd campus open house will begin at 9:30 a.m. on the north end of the Quad, followed by a traditional parade through the campus and downtown Davis. Campus departments, student groups, marching bands and the first annual "decorate-your-bike" contest will be the features of this year's parade. The parade marshals will be Dr. Peter Dietrich, a graduate of the UC Davis School of Medicine, and Ida Mae Hunter, the oldest known Davis resident at age 99. She has attended more than 40 Picnic Days. Dietrich is the medical director of the University Health Service in Berkeley. He received his bachelor's and medical degree from UC Davis in 1980 and 1986, respectively. "Down to Earth" is the theme of this year's celebration. UC Davis students chose the theme to coincide with the 25th anniversary of Earth Day, according to Devry Boughner, Picnic Day publicity chair. Attached is a schedule of events. Highlights for the day include: • Fifties rock 'n' roll and country music 11 a.m. at the Silo stage and Quad stage • Police dog agility demonstrations and the traditional dachshund races are among several different dog events scheduled 11 a.m. and 2 p.m. in and around Recreation Hall • Chemistry magic show noon in 194 Chemistry Building • Fashion Show 12:30 p.m. on the front lawn of Walker Hall • Battle of the Bands 2 p.m. on the Putah Creek east lawn • Soccer, water polo, volleyball, tennis, rugby and karate will highlight a day of intercollegiate athletic competition and sporting exhibitions. 10 a.m. to 6 p.m. at all athletic fields and Hickey Gym Dancing, department exhibits, a college bowl exhibition match and a body building exhibition are also planned. Food concessions will be available on campus, but no alcohol is allowed. This year's Picnic Day was organized by a 12-member student board of directors led by Heather Marshall.