A mother and her nine-year-old son lost in the rocky mountain forest of Sierra Nevada in the US state of California were rescued thanks to a trail of handwritten notes they left behind ? after getting stranded for more than 24 hours.

A search and rescue team found the pair on 12 July after discovering multiple notes tucked beneath rocks, left by the mother, aged 49. ?HELP. Me and my son are stranded with no service and can't call 911,? one said.

The pair were found by members of the Calaveras County Volunteer Search and Rescue Team, who already happened to be in the area.

The mother told ABC10 it had been a ?very scary experience?, but paid tribute to the ?amazing? efforts of the rescuers.

The mission was detailed in a Facebook post by the Calaveras County Sheriff?s Office.

On 11 July, someone phoned the Calaveras County Dispatch Center and informed officers that the duo were ?overdue? to return after departing for Camp Wolfeboro around 11:30 PST (18:30 GMT), the post said.

The mother and son were also not responding to phone calls, police were informed.

Speaking to ABC10, the mother, who identified herself as Tami, confirmed that they were unable to make any calls of their own, and that her son Stirling resorted to blowing his Cub Scout whistle in an effort to gain attention.

She had been attempting to drop off Stirling for a camping trip, she explained.

The police Facebook post said a volunteer search and rescue team already in the area for monthly training was soon deployed. It established a command post along the highway that leads to Wolfeboro.

?The team began assessing the terrain and the complex network of interconnecting, labyrinth-like roads to establish effective search parameters,? the post added. ?Air assets? and ?specially equipped? off-road vehicles were also used in the search.

A group of campers sent a text message to an emergency line telling police that they had seen a vehicle matching the description of the missing persons, which authorities said ?confirmed that the teams were searching in the correct area?.

Shortly afterwards, a rescue crew located the first handwritten message.

?We are ahead, up the road to the right. Please call 911 to get help for us. Thank you!? the message said.

The teams followed the road and found a second note, which included a telephone number and the names of the missing individuals.

Roughly a mile further along, officials found the mother and son.

Recounting the moment of their rescue, Tami told ABC10 that she first heard a vehicle honk. ?I turned around and I saw this truck coming down the road and It was just the best feeling ever.?

She and Stirling had spent the night in the car to avoid wild animals, and were lucky to have food, she added.

After locating the duo, the search team deployed vehicle recovery equipment to free their car and assisted them to return to waiting family members.

Officials determined the pair became lost in part due to a GPS signal that stopped working after they reached a remote area, leaving them unable to retrace their route. (BBC)

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