On January 22, 2000, about 1315 hours Pacific standard time, a Robinson R22B helicopter, N4072T, sustained substantial damage when it rolled over on departure from a dry riverbed near Piru, California. Group 3 Aviation operated the rented helicopter under the provisions of 14 CFR Part 91. The certified flight instructor and student were not injured. The local instructional flight departed Van Nuys, California, about 1145. Visual meteorological conditions prevailed and no flight plan was filed. The instructor stated he took his fiance up to introduce her to helicopter operations. After completing training they climbed to altitude to overview the river valley being used as a practice area, then descended back down. They observed an airplane flying low through the valley, so the helicopter landed in the riverbed to wait for the traffic to clear. After a few minutes the instructor prepared to liftoff. As he lifted off, the right skid stayed in contact with the ground and the helicopter continued to roll over to the right.