Police officers found the small horse munching on shrubbery in the front yard of a home near Seventh Street and Nevin Avenue around 3 a.m., police Detective Nicole Abetkov said.
Animal Services Deputy Director Rick Golphin said an on-call officer went to retrieve the horse and brought it to the agency's stables in Martinez.
He said Animal Services has previously picked up a couple of stray horses that wandered away from ranches near Giant Highway.
The agency is attempting to locate the pony's owner and is considering it a stray rather than an abandoned animal, he said.
Golphin described the horse as a "healthy looking" female white-and-brown pony estimated to be between 5 to 8 years old.