John Phillips, founder and chief songwriter of '60s folk-rock group the Mamas and the Papas, died Sunday morning at the age of 65.

The cause was heart failure, the Associated Press reported.

Phillips wrote or co-wrote the hits "California Dreamin'," "Monday, Monday," "Creeque Alley" and others for the Mamas and the Papas, which he formed in 1965 with his wife, Michelle Phillips, and "Mama" Cass Elliot and Denny Doherty.

John Phillips also organized the Monterey Pop Festival, the landmark 1967 concert that featured breakthrough performances by Jimi Hendrix, the Who and Janis Joplin, and set the stage for all rock festivals that followed. And he wrote the song that became the anthem for that year's summer of love, "San Francisco (Be Sure to Wear Flowers in Your Hair)"; it was recorded by Scott McKenzie, who played with Phillips in two of his early bands.

Following the 1968 break-up of the Mamas and the Papas, Phillips worked on solo material and struggled with a drug addiction that ultimately stifled his creative output. He and Michelle Phillips, whose marital troubles were chronicled in such Mamas and the Papas songs as "Go Where You Wanna Go," were divorced in 1970.

The band was inducted into the Rock and Roll Hall of Fame in 1998.

Phillips was the father of Wilson Phillips singer Chynna Phillips and of singer/actresses Mackenzie Phillips and Bijou Phillips. Mackenzie Phillips joined her father and Doherty in a regrouped version of the Mamas and the Papas in the early 1980s.

"We are all mourning the loss of my dad. He was a genius and a good man and will be missed," Mackenzie Phillips said Sunday in a prepared statement, according to Reuters. "I spent the morning with my sisters Chynna and Bijou. We are all on our way to the beach where we will walk and swim and celebrate our father's life."