A bicyclist seriously injured last weekend in a Sonoma Valley collision with a car apparently was at fault because he crossed into the opposite lane on a curve, the CHP said Monday.

Christopher Lyman, 43, of Napa was flown Saturday by REACH helicopter to Santa Rosa Memorial Hospital, where on Monday a spokeswoman said he was in serious condition.

The CHP said Lyman was riding west on Trinity Road at 10:20 a.m. Saturday when just west of Cavedale Road he headed downhill and on a curve crossed over the double yellow lines and collided with an oncoming car.

Lyman was thrown from his Specialized bike and landed on the 2007 Toyota Corolla driven by Sheryl Hartman, 56, of Sonoma.

Hartman wasn't reported injured.