John "Marmaduke" Dawson had original tunes in his pocket and a guitar in his hands in 1969 when a buddy just learning to play pedal steel guitar often joined his weekly gig at the Underground, a San Francisco Bay Area hofbrau house.

The friend was Jerry Garcia of the Grateful Dead, and those sessions set the stage for the New Riders of the Purple Sage, a group they considered "the original psychedelic cowboy band."

Mr. Dawson, 64, died Tuesday of stomach cancer in San Miguel de Allende, Mexico, said Buddy Cage, who has played pedal steel guitar with the group since Mr. Garcia left in 1971. Mr. Garcia died in 1995.

The New Riders initially gave Mr. Garcia and two other members of the Grateful Dead -- Mickey Hart on drums and Phil Lesh on bass guitar -- a way to further indulge their taste for country music. But Mr. Dawson's songwriting skills quickly helped the offshoot band develop an independent country-rock identity.

Rob Bleetstein, archivist for the New Riders, wrote in an e-mail, "Dawson's songwriting brought an incredible vision of classic Americana to light with songs like 'Glendale Train' and 'Last Lonely Eagle.' "

With that material and such other "wonderful" Dawson songs as "Garden of Eden" and "Henry," the band "simply had to become a reality," Dennis McNally, a Grateful Dead publicist, said last week on Relix magazine's Web site.

They toured with the Grateful Dead, as the psychedelic rock band's opening act from 1969 to 1971, then became successful touring on their own, Mr. Bleetstein said.

In 1974, the New Riders played a free concert for an estimated 50,000 fans in New York City's Central Park.

According to the "Encyclopedia of Popular Music" (1998), their first, self-titled release "blended country rock with hippie idealism, yet emerged as a worthy companion to the parent act's lauded 'American Beauty.' "

Mr. Dawson had written every one of the album's tracks.

With Mr. Dawson as the lead singer, the New Riders released eight albums on Columbia Records from 1971 to 1976. Among their most popular releases was 1973's "The Adventures of Panama Red." The title track, written by Peter Rowan, was one of the New Riders' bigger hits.

The band's lineup changed over the years, but Mr. Dawson and another founding member, singer-guitarist David Nelson, stayed with the group until it essentially broke up in 1982. Mr. Dawson continued performing with a band built around the name New Riders of the Purple Sage until the mid-1990s.

A son of privilege, John Collins Dawson IV was born in 1945 in San Francisco.

At the home of his guitar teacher -- who was his best friend's mother -- Mr. Dawson met Mr. Garcia around 1959, Mr. Dawson recalled in a history on the band's Web site.

Later, he often ran into Mr. Garcia at a Palo Alto music shop where Mr. Garcia rented space to give music lessons.

In 1965, he was hanging out with friends when one of them dubbed him Marmaduke, for no apparent reason. The nickname stuck but Mr. Garcia later shortened it to "McDuke," Mr. Dawson wrote, because he could "talk like Donald Duck."