The Valley of Gwangi
(1969)

Before Cowboys vs Aliens, there was cowboys vs. dinosaurs.

Some cowboys are running a dilapidated rodeo in a small southwestern town.  They learn of a valley where prehistoric animals still live.  They capture a T Rex to put in their show, naming him Gwangi.  

The local gypsies know of the hidden valley, and are furious that anything has been removed from there.  One of the gypsies sneaks in, and frees Gwangi.  Gwangi goes on a rampage, causing a stampede of people trying to escape. The church catches fire.  They lure Gwangi into the church, and lock him in.  The burning church collapses, killing Gwangi.

Thanks Joseph C!