Tom DeSantis of Temecula emailed that his 15-year-old son Alex had stumped him with a question about our area and hoped I could help.

“He asked me about the structures that appear to look like cement smokestacks at the east end of Murrieta Hot Springs Road and Butterfield Stage Road,” wrote DeSantis. “There are also several sets of two such structures looking northeast from that intersection.”

I’m here for you Alex.

This is actually a timely question and one that is sure to be asked as work wraps up this spring on the extension of Butterfield Stage Road in the area and more and more houses are built near a pair of these “smokestacks” along Murrieta Hot Springs Road.

My initial reply was “I don’t know.”

With assistance from my colleague Aaron Claverie, we contacted Greg Butler, Temecula’s assistant city manager who had previously served as the city’s public works director, and got an answer.

“My understanding is that those are the vent pipes for Air-Vacuum Release valves, commonly referred to as Air-Vacs, for the large diameter MWD (Metropolitan Water District) transmission lines that pipe water south toward San Diego,” Butler replied. “These devices are installed at highpoints in water pipelines as that is where any air trapped in the pipeline tends to accumulate. The Air-Vac will release the air out of the line to prohibit corrosion at this point.”

A little more background here, provided by yours truly.

Most of us think of Lake Skinner, east of Temecula, as a bucolic spot for fishing, camping and the home of the annual Temecula Valley Balloon & Wine Festival.

However, the man-made lake was built in the early 1970s as a storage facility for water headed to San Diego.

I know, just another example of Riverside County carrying water for folks in San Diego.

Colorado River water flows into Lake Skinner and is sent south underground via the “Second San Diego Aqueduct” from Skinner’s filtration plant through open country – most of it restricted habitat — east of French Valley Airport, reaching Temecula’s city limits near the east end of Murrieta Hot Springs Road.

The Air Vacs in the area of Murrieta Hot Springs Road are pretty darn tall and if you stand near them – as I did on Thursday — you can hear air pressure being released.

“My understanding is that the bigger the pipe and the greater the pressure … the taller the vent pipe needs to be,” wrote Butler.

Much smaller versions of Air-Vac outlet pipes are part of most water pipelines, Butler added.

“They are typically on the side of the road with a protective pipe-like cover over them with air holes punched in them,” he said.

The 94-mile Second San Diego Aqueduct was actually built in 1960 before the Lake Skinner storage facility.

In many areas the second aqueduct parallels the older San Diego Aqueduct, built in the 1940s, which also brings Colorado River water from a portal near Hemet, under Temecula to San Diego, but does not feed into Lake Skinner.

Gravity carries the water through Temecula, under familiar landmarks such as the Temeku Hills Golf Course, Rancho California Road, Temecula and Pechanga parkways and a sliver of the Temecula Creek Inn Golf Course.

The second aqueduct parallels Interstate 15 into Rainbow and San Diego County. It then winds through that region with a final destination of the Otay Reservoir in southern San Diego County.

Glad to answer your question Alex.

As always, if you got a question about the odds and ends of Southwest Riverside County, let me know and we’ll figure it out somehow.

Contact columnist John Hunneman at 951-368-9693 or jhunneman@pe.com