The 16-year-old was exploring the Old Barrington Quarry in Martin,about 30 kilometres from Perth,when witnesses say he slipped and fell off a bridle trail.
He was rescued by the RAC Rescue helicopter around 2pm.
Witness Emil Tonsberg told 9 News Perth the teen suffered a serious hip injury and broken arm.
“We think he might have damaged his neck or spine,” he said.
“He was grabbing for branches,and he didn’t get it fully with his hand and he started sliding with his feet,and then he started sliding further down and lost control.”
The teen was taken to Royal Perth Hospital where he was in a stable condition on Wednesday morning.
The boy’s rescue follows.
It is understood the eight-year-old had fallen a long distance from rocks at the popular waterfalls in Perth’s east.
He was winched out and taken by RAC Rescue chopper to Perth Children’s Hospital where he is currently in a stable condition.