'Big Bang' Star Johnny Galecki's Home Burns Down in Massive Fire

"Big Bang Theory" star Johnny Galecki's ranch burned to the ground Monday night in a huge fire in San Luis Obispo ... TMZ has learned.

It's Johnny's getaway place ... 190 miles from L.A. The ranch was torched along with other property in the 1,200 acre fire, that's now 40% contained. We're told the area is secure and no one can enter for now ... the road is closed.

Our sources say Johnny hasn't seen the property since it burned down, and plans to show up when he gets the all clear ... so he can salvage anything that was spared.

Johnny tells TMZ, "My heart goes out to all in the area who are also experiencing loss from this vicious fire, the threat of which we live with constantly, which may seem crazy to some but we do so because living in our beautiful, rural area makes it worthwhile."

Johnny goes on ... "It's never the structures that create a community -- it's the people. And if the people of Santa Margarita have taught me anything it's that, once the smoke has cleared, literally and figuratively, it's a time to reach out and rebuild."