He rejoined the band in 1994 and has been with them ever since.
The group, famous for the multi-platinum selling albums "Cocked and Loaded" and "Hollywood Vampires," who will perform at Park City Live on Thursday, Oct. 25, is celebrating 25 years in the business.
However, Riley has been playing the drums professionally for almost 40 years.
"I'm a little older than the other guys in the band and have been a recording musician since 1975, but I've been playing drums from almost 50 years. I was born in 1956, and started playing when I was six," Riley said during a phone interview from his home in Los Angeles, Calif. "So, I can honestly say I was into Buddy Rich and Gene Krupa."
During his teens, Riley experienced, like his peers, the joy of seeing the Beatles on Ed Sullivan and the whole British Invasion of the 1960s.
"I was influenced by those drummers from Ringo (Starr) and Charlie Watts to my idol Ginger Baker and Mitch Mitchell and John Bonham," Riley said. "The funny thing was I never wanted to play drums to be a rock star. I just wanted to make a living playing, whether it was in jazz, progressive rock or hard rock. I just wanted to see if I could do it as a profession."
Riley's rock-music career began when he started signing on with various groups or artists in the L.A. area.
He started with a band called Roadmaster and had worked his way through other groups such as The Lawyers, B'zz, Keel and W.A.S.P., before landing his gig with L.A. Guns.
"I was only 18 when I signed that record deal with Roadmaster," Riley said. "From that point on, all the way up to W.A.S.P., I did things with groups that were mainly one-off album bands that didn't go very far."
With each band, Riley learned he had to make some difficult decisions that would eventually benefit himself.
"In this business, if you want to make it and move on, you have to learn how to walk away from a one situation into a better one," he said. "That's a difficult and emotional thing because I've gotten into a group with people that I liked, and wrote a lot of songs with them just trying to make it big.
"But you do need to have that cold streak in you to be able to leave if a better situation comes along," he said.
One example of that came when Riley was in Keel in 1983.
"It was during the first wave of metal that came out of L.A. with Motley (Crue), W.A.S.P. and Ratt," he said. "Keel was one of those bands and they asked me to join."
The band was in the studio working with Kiss' Gene Simmons on the album 'The Right to Rock' on A&M Records.
"It was a great scene and I recorded songs for the album and did some background vocals with Gene," Riley said. "Before that album was completed, I got a call from W.A.S.P. to join them for their first world tour."
Although the decision was difficult, Riley decided to head out on the road with W.A.S.P.
"I had to make a call for myself and left a great situation, but I think I made the right call," he said. "I may not have joined L.A. Guns if I didn't join W.A.S.P."
Riley joined L.A. Guns in 1987, replacing Nickey "The Beat" Alexander, and is considered part of the classic lineup that included lead guitarist Tracii Guns, rhythm guitarist Mick Cripps, vocalist Phil Lewis and bassist Kelly Nickels.
Although the band hit it big thanks to the popularity of the late 1980s' L.A. Strip, MTV's Headbanger's Ball and rock radio, when Riley joined, it was still paying dues small pubs.
"The last gig I played with W.A.S.P. was headlining the Long Beach Arena, and my first gig with L.A. Guns was back in a club," he said. "Most people I know would not have done that, but when I joined L.A. Guns, I saw something cool was happening. They were on the cusp of the new wave of the Los Angeles metal scene.
"It was big step forward for me and I'm a lucky guy, because there ar a lot of talented people who haven't had the opportunity to do what I have done," he said. "I feel fortunate to be involved in the involved with the entire L.A. scene."
Riley was able to participate in the band's classic-lineup reunion 1994, and have stuck with it throughout the subsequent lineup changes.
The musicians who comprise L.A. Guns today are Riley, vocalist Lewis, guitarist Stacey Blades and bassist Scott Griffin, and they still play shows all around the world.
To celebrate its 25th anniversary, the band recorded a new CD, "Hollywood Forever," produced by Andy Johns, who produced the past four of five recent L.A. Guns CDs.
"We're fortunate to still be out there playing, and we hope people will come to the Park City show, because I think we'll be on fire," Riley said.
L.A. Guns will perform at Park City Live, 427 Main St., on Thursday, Oct. 25, at 9 p.m. Tickets are $17.50 and available at www.ticketcake.com.