NAZARETH, Pa. -

When the fall term begins at Nazareth Area High School on Monday, one teacher will be conspicuous by his absence.

Matthew Greene was a popular math teacher at the school when he vanished while on a backpacking trip in California last month.

Police say the 39-year-old Greene was in California to hike and climb the Eastern Sierra, a region that features extremely steep and rugged terrain. The last time anybody heard from him was July 16.

His disappearance has baffled friends and family who call Greene a highly experienced, cautious outdoorsman.

Searches of the vast wilderness for the former Peace Corps volunteer have thus far been unsuccessful.

A hiker recently found a pair of eyeglasses that might belong to Greene.