When we lived in Granada Hills, there was a great horned owl that regularly perched in a big pine tree on the property. Once during the daytime I saw a young hawk in the same tree, screaming at the owl in fear or fury. The owl just sat there, apparently unperturbed, while the hawk gradually backed away and eventually flew off. Usually, though, the owl was only seen at night; we'd spot it in silhouette when it landed in the tree. Sometimes we'd hear its calls and the responses from a more distant bird.
But in ten years in West Hills, we've had neither sight nor sound of an owl, until last night. I woke up around 3:30 am to repeated calls. If there were any replies, I couldn't hear them.
This area provides a good living for birds of prey. There are rabbits, rats, mice, lizards, and small birds of all kinds. We see hawks every day, and on a few occasions, kestrels. I'm sure there have been owls here all along, but they have managed to remain unknown until now.
At WhatBird, you can search for "great horned owl" and find out exactly how they sound.