The Battle of Topanga Canyon was a battle in The War Against the Machines (SCC Timeline) in 2027. This was one of the first battles in which reprogrammed Terminators were used. It involved John Connor taking a lot of men and weapons into this battle. After capturing the base, he and Kyle Reese went with a small group deep into a facility in Topanga Canyon. They left some men outside to guard the entrance. After a couple days, they came out of the facility and John told them to blow the place up. It is inferred that Kyle Reese was sent on his time traveling mission to 1984 in the facility, since he never returned. Soon after the battle, Derek Reese was told about the battle by Sumner.
Sumner: They found some Skynet complex in Topanga canyon. And decided to put all the firepower we had into it. We lost a lot of men.
Derek: What was it?
Sumner: I don't know. Some kind of research facility, factory, something. No one would tell us. Connor took a small group, including your brother, deep into the place. Left the rest of us outside to guard. A couple days later, he came out. Ordered us to blow the place to hell.
Derek: So what about Kyle? What happened to my brother?