Jet Aircraft Mix Oxygen with their fuel,Hence the The Large intake ducts/fairings on Jets of Today! Short of Cruise missles,of which are Too Slow to produce a Distinguished line,Arcing Upwards,It was Definitely a Solid-Fuel Rocket motor of some kind,The Contrail was Huge & Quite Visible,Something like a Trident Missle-SLBM,The residual contrail Floated over LA,& Was Quite Visible,Especially towards Sunset!LA Has seen it's Share of Ballistic launches,This was No Different,Other than It's course seemed to be headed North West!