Two minutes later, the second stage engine shut down as planned and two-and-a-half minutes after that, the SAOCOM 1A satellite was released into the planned polar orbit. One of those viewers was Los Angeles mayor Eric Garcetti.
This marked SpaceX's 30th landing of a first stage, as well as the first time a Falcon 9 rocket touched down on the West Coast.
By the way: SpaceX would like to land every booster on terra firma, to ease the reflight process.
From the ground, Twitter users posted incredible shots of the Falcon 9 coming back to Earth. Prior landings have taken place on the East Coast.
The launch is scheduled for shortly after 7:20 p.m., Vandenberg Air Force base officials said in an advisory.
Argentina's domestic satellite manufacturer INVAP built the satellite with assistance from other agencies and domestic companies.
SAOCOM 1A carries a high-resolution instrument called a synthetic aperture radar that will be used for emergency management during disasters and for land monitoring.
As the biggest antenna in space for a civil mission, its main objective is to gather soil moisture information. Both spacecraft will make similar observations from orbit, which will be integrated with measurements made by a network of Italian satellites.
The company is contracting with NASA on several ventures and one of SpaceX's spacecraft was the first private spacecraft to dock at the International Space Station.
"SAOCOM" is short for "Satélite Argentino de Observación Con Microondas", which is Spanish for "Argentine Microwave-Observation Satellite".