Taken from a website: William Mulholland (September 11, 1855 - July 22, 1935) was the head of the Department of Water and Power in Los Angeles, CA. He was responsible for building the water aqueducts that allowed the city to grow into one of the largest in the world.
These last 2 photos are borrowed from a site that said it was ok to copy. This pic looks to be before the renovation.
Update (More info): Today 10/24/09 I had a customer come in and while I was faxing his papers for him, I noticed he had on a t-shirt from the Department of Water and Power. I asked him about it and he told me he's been retired for about 11 years but that he was 3rd generation working for them. His Grandad and father had both worked there. I told him I had started a blog and that just yesterday, I had taken pictures of the fountain and wrote about it on my blog. He told me that under the fountain there is an electrical switching station and he remembers going there with his dad when he was a young kid. It's a large room with all kinds of controls all around. He doesn't remember how he got down there exactly but he does remember steps. Geez, I never knew there was an underground room under that fountain. See... ya learn something everyday!