The crosses were created by retired Chicago carpenter Greg Zanis, who also made 58 crosses in honor of the Las Vegas mass shooting victims.
RELATED: Thousand Oaks shooting: Big brother-to-be, soon-to-retire sergeant among the victims
The 12 crosses were placed just outside the Borderline Bar & Grill. The crosses have the names of all 12 victims killed in the mass shooting.
The crosses make up part of a makeshift memorial outside the nightclub. Area resident Michelle Kam-Biron came out to the memorial to pay her respects Monday morning.
She said she read about the crosses on a Facebook post.
MORE: Mom of Thousand Oaks shooting victim calls for better gun control, no longer wants 'thoughts and prayers'
"I was just touched that someone from across the country could feel the pain that we're feeling here in Thousand Oaks," Kam-Biron said. "That he sacrificed all that time and trouble and made all these crosses for these victims of such a tragic and terrible event that happened - it was just touching, and that's what brought me out here."
Kam-Biron described the massacre as "senseless."
"The guns...I don't want to get into politics, but it's terrible, losing one's life over such a senseless act," Kam-Biron said.
PHOTOS: Mass shooting at nightclub in Thousand Oaks, California