Fires of unknown origin caused extensive damage to two Fairfax County homes yesterday, fire officials reported.

The most serious fire did $150,000 damage to an unoccupied home at 10812 Hunt Club Rd., Reston, authorities said. The roof of the house, owned by Warren Pat Nobles, was destroyed and the interior was extensively damaged, according to officials.

Nobles and his family were not at home at the time of the blaze, which officials said started on the first floor at about 4 p.m. Cause of the fire is under investigation, officials said.

In the other blaze, archeologist Bruce D. Smith was sitting in the living room of his detached single-family home at 2404 Daphne La. in the Hollin Hills section of the county at 10 a.m. when he saw smoke in the kitchen, he said yesterday. "The fire had started in some discarded Christmas wrappings and boxes in the trash outside the house," said Smith, 34, a curator at the Smithsonian Institution'Museum of Natural History.

Fairfax County fire officials said the fire caused $50,000 damage. CAPTION: Picture, Only a chimney stands after a fire destroyed the roof and damaged the interior of an unoccupied home at 10812 Hunt Club Rd. in Reston, causing $150,000 damage. By Fred Sweets -- The Washington Post