He’s a gem of a guy.

An honest New Jersey man who found a backpack stuffed with about $18,000 worth of jewelry and $5,000 in cash at a Ramapo State Forest parking lot tracked down the woman who owned it — and returned it to her.

“I thought I would try to do the right things through life, and that was the right thing to do,” Joseph Monto, 33, a substation mechanic for PSE&G, told The Post yesterday.

Monto, his pregnant wife Ilmadeliz and their 15-month-old son, Frank, of Ringwood, were driving along Skyline Drive at 6 p.m. Sunday when he spotted a blue backpack at a parking lot used by hikers.

“I thought maybe someone left their wallet, and I could do them a favor and call,” said Monto, who was shocked when he found a case inside the backpack “stuffed with money and jewelry.”

“I said, ‘Oh, my God!’ ” I thought it might be a burglary,” said Monto, who took the backpack home for a closer look. He saw notebooks and papers with GPS coordinates and what looked like codes.

“I thought, ‘Oh my goodness, hopefully it doesn’t have to do with terrorists,’ ” he said.

Monto soon turned up contact information that led to the woman’s brother — and then to a grateful Rebecca Knox.

“She was like, ‘Thank goodness you found it! You restore my faith in humanity. There still are good people out there,’ ” Monto said.

The Maine woman was in New Jersey to help her parents move into a retirement community, and the $5,000 was a down payment for their new home, according to The Record newspaper .

The Record said she takes the jewelry pouch — which held a platinum watch, a pearl necklace and gifts from her husband — when she travels.

The GPS coordinates and “codes” are part of a treasure-hunt game called “geocaching” that uses the coordinates to look for hidden “treasures.”

She spent part of Sunday in the park, and must have lost the backpack when she took it out of her car to look for her cellphone, she told The Record.

That very night, Knox and Monto met at the parking lot and he returned the backpack.

She later sent him a thank-you note and a check for $1,000 that Monto says he’ll use to finish a bedroom for the couple’s second child, due in early March.

rita.delfiner@nypost.com

