By Homer Clance, San Diego Union Staff Writer PALM SPRINGS — Lawmen yesterday routed the youth invasions that had engulfed this normally placid desert resort. Hundreds of youths and hippies were ousted from their camps in rugged, rocky Tahquitz Canyon, where they had settled earlier in the week. They were among the 20,000 young persons who flooded the town for the Easter vacation. A city ordinance prohibits camping or campfires in the beautiful canyon, which has a waterfall and stream. City regulations prohibit anyone in the area after dark. Advertisement Copter Orders Youths Out A helicopter on loan from the Los Angeles Sheriff’s Office circled the area yesterday and ordered the invaders to leave. A sergeant notified them they were violating the law and would be arrested if they did not move on.