One person killed in a chain-reaction collision in Contra Costa County Saturday morning was part of a large group of bicyclists traveling in the area.



California Highway Patrol officers say the cyclist died when his bike collided with a water truck around 9:45 a.m. on eastbound Highland Road about three-quarters of a mile west of Carneal Road.



The bicyclist, a 40-year-old Dublin man, was part of a large group of at least 50 bikers. According to Officer Greg Hartt, there were two separate accidents that happened moments apart.



First, two of the riders at the front collided. "Near the end of the pack, as people were swerving to avoid the collision at the front, at some point another rider, unknown at this time why, crossed over the double yellow lines and collided with a water truck," Hartt said.



He was riding a Specialized bicycle and wearing a helmet, according to the CHP.



The truck driver, a 56-year-old Livermore man, driving a 2001 Peterbilt truck, saw ahead of him the bicyclists at the front of the pack crash and veered to avoid them. That is when he struck the bicyclist who was in the roadway, along with his bicycle.



"He saw a lot of bicyclists scrambling to avoid the first collision and, at that point, he did see somebody come into the lane in front of him and he tried to stop as best he could and was unable to avoid him," Hartt said.



Many cyclists tried to help the struck man, but emergency personnel pronounced him dead at the scene.



Another person suffered major injuries and a third bicyclist suffered minor injuries, CHP officials said.



The truck driver was not injured, according to the CHP. He was wearing a seatbelt during the incident. Drug or alcohol use is not suspected as factors in the crash, according to the CHP.



Highland Road was closed for three hours after the crash.



Other cyclists say this area of unincorporated Contra Costa County is a popular spot for weekend rides.



"Almost every Saturday morning, there's at least three or four large groups that come down," bicyclist Jim Frahm said.



The victim's name has not been released. The others involved in the initial collision are being treated at the hospital.