T The tree fell on the west side of the highway south of Spencer Avenue at about 7:20 a.m., hitting an electronic message sign then striking a black Honda Fit in the slow lane, CHP Officer Andrew Barclay said.
The Honda, driven by Anthony Contini, 70, of Mill Valley, spun out of control and stopped facing north on the right-hand shoulder, Barclay said.
The tree also struck a gold Toyota Camry in the No. 2 lane -- the second lane from the left -- and landed across the No. 2, 3,and 4 lanes, Barclay said.
The Toyota's driver, Ellyn McCaffrey, 47, of San Anselmo, got out of her car and went to the right shoulder where it was safe, and Contini remained in his Honda, Barclay said. Neither driver was injured or taken to a hospital.
The Honda sustained major damage, and the tree shattered the Toyota's windshield and damaged its right side, according to Barclay.
The CHP, the Southern Marin Fire Protection District and a Golden Gate Bridge patrol unit responded to the incident.
A tow truck was unable to move the tree out of the lanes, so Southern Marin fire personnel used a chainsaw to cut it into smaller pieces which were then carried away, Barclay said.
Three lanes of the highway were blocked after the tree fell, causing traffic to back up more than 6 miles to Paradise Drive in Corte Madera, Barclay said.
Caltrans was notified of the incident and will be responsible for inspecting the hillside, Barclay said.