Hell Angels attacking fans at Rolling Stones concert at Altamont, California in 1969 Photograph: Michael Ochs Archives./Michael Ochs archives/Redferns

ALTAMONT, CALIFORNIA, DECEMBER 7

Thousands of shivering people awoke this morning in the chilly fog draped around these arid hills, 40 miles south of San Francisco, and continued picking up the pieces in the wake of the largest free rock concert in the history of the western United States. The stragglers had been trapped by the massive three-day traffic jam that resulted when more than 300,000 people went to the Altamont motor racing track for the great alfresco happening yesterday by an appearance of the Rolling Stones.

Four young men had died violently by the time the concert ended last night. The Red Cross, however, reported four births at the raceway. Dozens of people were treated at emergency medical centres for everything from bad drug "trips" to blisters. By early yesterday afternoon doctors were forced to send out an emergency call for thorizene, a sedative that mitigates the bad effects of hallucinogenic drugs. Supplies were flown to the site by helicopter from a near-by hospital.

Although the air was filled with the acrid sweet smell of marijuana, the majority of those at the massive encampment comforted themselves with beer and cheap wine. The atmosphere was generally friendly and free-wheeling with people sharing the food and drink they had brought with them. One death was attributed to a knife attack on an unidentified young man by a group of "Hell's Angels" motor-cyclists. Another youth drowned when he fell into a swiftly moving irrigation canal and two more young men were killed as a car ran over them in their sleeping bags last night. The concert billed as "Woodstock West" was originally to be held at Golden Gate Park in San Francisco, the scene of last month's moratorium day peace rally. During swift negotiations after city officials decided they could not handle the expected crowds, the site was shifted first to the Sonoma County wine-growing district north of the city, and finally to this uninhabited moor overlooking the Livermore Valley, where the free use of the automobile track was offered by the owners.

The Rolling Stones were the chief attraction, although the programme included 20 other groups including the Jefferson Airplane and the Grateful Dead. It was the climax of the first American tour for the Stones in three years. Mick Jagger, the lead singer, seemed nervous at first about the size of the audience, but the response soon changed all that. When a young girl broke on to the stage nude during the performance of "Satisfaction", Jagger stayed well across the makeshift stage until she was hustled away.