A grass fire burned up 150 acres just outside a subdivision east of Brighton Saturday evening, firefighters said.

Brighton Fire told 9NEWS the fire was fast moving and even changed direction - threatening homes and horses nearby.

It took about an hour and a half to get under control - when the fire was finally contained people and horses were able to return to their pastures.

Brighton Fire was assisted by South Adams and Southeast Weld fire crews. Adams County Sheriff's Office is going to investigate the cause.

Steve Jenkins, a resident of the Hayesmount subdivision off 29700 E. 163rd Place, said he, earlier on Saturday, mowed the grass where the fire happened.

"There's no fuel and the fire just burned all the fuel right up to the clear way, and fortunately there wasn't anything left to burn," he said.

The fire happened on 400 acres of undeveloped land, burning up about half of it.

Jenkins said flames were as tall as the homes nearby.