Originally Posted by Stanford_1K
Or, for that matter, I don't think you even have to "close" the circle by going back to DSM, so long as the "open" part of the circle is the shortest leg. (Others will correct me if I'm wrong about this, and it may depend on the combinability rules of your particular fares.) So you could book DSM-BWI-SMF-xxx where the distance xxx-DSM is less than DSM-BWI (your shortest segment). So try, for example, DSM-BWI-SMF-ORD or DSM-BWI-SMF-DEN or DSM-BWI-SMF-IAD.
I think you might be confusing the two concepts.
An open jaw can only have two segments--well, not really segments, but two fares. That is, say: LAX-JFK-SFO or JFK-LAX/SFO-JFK where LAX-SFO is a surface segment and is not flown.
A circle trip is where you have more than one destination but a single origin. Say, LAX-IAD-ORD-LAX where LAX is your origin and you stop in IAD & ORD, not just connect. Of course, your origin, or even connecting points could be co-terminals, but for the sake of simplicity, lets forget about that for the moment.
What you are proposing is a combination of the two, and I don't think such exists as far as fare rules are concerned. Most engines would just price out a bunch of one ways, although an intelligent booking engine, or a human TA, might suggest a one way + an open jaw. So, for your DSM-BWI-SMF-ORD example: DSM-BWI as a one way, then an open jaw BWI-SMF-ORD which should price cheaper in most circumstances.