Happy Face Hill mystery illuminated by a Simi Valley family

A monthlong mystery over who illuminated the big grin on Simi Valley’s Happy Face Hill has been solved: Two sisters, ages 3 and 7, did it.

“They wanted to surprise me because they knew how much I love the happy face,” said their mother, Allison Robertson of Simi Valley.

Robertson is a business administration student at Moorpark College who tries to do her studying on weekends. Her husband, Doug, takes Tabitha and Evelyn on Saturday jaunts to give her some peace when she hits the books.

“I need a big chunk of quiet time,” said Robertson, 29. “So they do things like have ‘silly-pic Saturdays’ where they go out and take pictures around town. They go on hikes. It gives me enough time to study.”

Earlier this month The Times detailed how a Northridge man in 1998 created the smiley face next to the 118 Freeway near its entrance to Simi Valley and how in January a Chatsworth restaurant owner installed solar-powered garden lights on its grin and eyes. The story noted that no one knew who was responsible for outlining the face with solar lamps, however.

That report prompted Robertson to fess up about her daughters’ weekend jaunt six weeks ago when they added lights to the face’s edges.

Doug Robertson, a 38-year-old electrician, said he got the idea to involve the girls while driving home from work after dusk. “I saw there were lights on the eyeballs and mouth. I decided we’d do something crazy.”

Robertson said he bought 36 garden lamps for $1 each at a discount store and asked the girls if they wanted to install them. “They were gung-ho to go,” he said.

On the day of the installation, “we had trail mix for a snack, but the chocolate in it melted on the way up the hill,” said Evelyn, a second-grader at Katherine Elementary School.

Once at Happy Face Hill, Robertson turned the event into an impromptu math lesson as his girls counted their steps as they walked around the face’s circumference. “It turned out we had enough lights to put one every four adult-size steps,” he said.

That night, the girls and their dad took Allison Robertson out for dinner. On their way, they detoured past Happy Face Hill where the huge smiley face was aglow.

“We did that for you, Mom!” the girls shouted out.

Doug Robertson said his wife was pleased — but a little nervous.

“My wife’s a goody two-shoes. She only ditched school one time in her life, and before she did that she asked her mother if it would be OK,” he said.

“So she asked if we trespassed when we put up the lights.”

bob.pool@latimes.com