Daniel Arias, 25, of Tujunga was arrested Tuesday and was booked on suspicion of animal cruelty, police said. He's being held in lieu of $20,000 bail.
The shocking incident was captured on surveillance video, which surfaced on March 27. It shows the driver of a Chevy Tahoe pulling up near the wash and pulling a crate containing the small black dog from the back.
Moments later, the driver throws the cage over a fence into the wash.
"We were in our yard and we heard a lot of commotion, screaming, you know, dog kind of screaming," said resident Jim Tavare.
Tavare said when he walked over to the wash, he saw the cage in a corner of the storm channel but the puppy wasn't inside.
A short time later, he saw a message about the incident on a social media app. That's when several people rushed to the wash and started searching the area before a neighbor finally rescued the dog.
"They found the dog fairly rapidly, in about half an hour, I think," said Tavare. "They came down the hill with it and it had been hiding in the drain. I couldn't believe someone would do that."
The puppy has since been placed in the care of Los Angeles Animal Services.
In a tweet, LAPD expressed gratitude for the outpouring of love from the community, saying, "The puppy will soon be available for adoption to a loving home."
Anyone with additional information was asked to contact the LAPD Foothill Division at 818-834-3115. Callers who choose to remain anonymous can contact Crime Stoppers at 800-222-8477.