The reptile, which is native to Africa, is now being held at a Riverside County animal shelter.
Riverside County Animal Services said he's someone's pet who apparently got out.
"The residents were freaking out because here's the Godzilla-like creature walking down the sidewalk," said John Welsh, spokesman for Riverside County Animal Services.
After a frantic 911 call and some quick work with a catch pole, the lizard was captured and brought to the shelter, where he'll stay until his owner shows up.
Black-throated Monitor lizards are carnivorous, legal to own in California and native to the African grasslands and parts of Asia. Juveniles go for about $100 in pet stores, but they grow.
Back at the shelter, staff found the reptile was well-behaved for a Monitor lizard.
The Associated Press contributed to this story.