Running back Frank Gore, who left the San Francisco 49ers to sign with the Indianapolis Colts last week, offered a message Monday to the 49ers and their fans.

“As I look forward to an exciting new opportunity, I cannot help but reminisce about the past 10 years in the Bay Area,” Gore said. “I would like to, once again, thank the York family and the 49ers organization for giving me the opportunity to realize my childhood dream of playing in the NFL. I am truly thankful to all of my 49ers teammates, coaches and staff that have helped me reach milestones and strive for greatness over the years.

“And to my fans: I do not know where to start. There are no words to describe how appreciative I am of the support and encouragement each and every one of you has provided. I will always carry you with me. Thank you for everything.”

Gore, the 49ers’ career rushing leader, signed a three-year, $12 million contract with the Colts last Tuesday.

Gore was expected to sign with the Philadelphia Eagles. He agreed to the framework of a three-year, $7.5 million contract the weekend before free agency started, but he changed his mind when the Colts became a possibility.

“(Eagles coach) Chip (Kelly) is a great coach, but my option was to always want to be (in Indianapolis),” Gore told the Colts’ website. “I had to follow my heart. Every time I follow my heart, I’m doing the right thing.”

Gore said he chose the team that gave him the best chance to win the Super Bowl.

“It was very tough. I’ve been in San Fran for 10 years. A great organization,” Gore said. “I know at this point of my career I want to be with a team that’s got a shot to get the trophy. In this game, when you’re done, you want to be able to hold the trophy. I think, on the field, I can help this team out a lot.”

In 10 seasons with the 49ers, Gore set team records with 11,073 rushing yards, 64 rushing touchdowns and 38 100-yard rushing games. He is third in total touchdowns (76) behind Jerry Rice (187) and Terrell Owens (83).