SEASHORE: A pair of hikers fell roughly 70 feet when a section of bluff crumbled on Saturday at the popular destination. The park had posted warning signs just over a day before the collapse.    Courtesy NPS

A section of a high bluff at Arch Rock in the Point Reyes National Seashore crumbled on Saturday, killing a San Francisco preschool teacher and seriously injuring her hiking companion. The overlook had developed a wide, 40-foot long fissure last Thursday, seashore spokesman John Dell’Osso said.

Arch Rock, carved from the base of the overlook . . .