It's implied to often that America has all the same gun laws across the board and you can just walk in anywhere and anyone can buy anything (gun wise) and that simply is not true. Let's take this instance, it was in California. Not Florida or Texas.
The gun laws of California are some of the most restrictive in the United States.
A Firearm Safety Certificate, obtained by passing a written test, is required for gun purchases. Handguns sold by dealers must be "California legal" by being listed on the state's Roster of Handguns Certified for Sale. This roster, which requires handgun manufacturers to pay a fee and submit specific models for safety testing, has become progressively more stringent. Private sales of firearms must be done through a licensed dealer. All firearm sales are recorded by the state, and have a ten-day waiting period. Unlike most other states, California has no provision in its state constitution that explicitly guarantees an individual right to keep and bear arms. The California Supreme Court has maintained that most of California's restrictive gun laws are constitutional, based on the fact that the state's constitution does not explicitly guarantee private citizens the right to purchase, possess, or carry firearms.
Semi-automatic firearms that the state has classified as assault weapons, .50 BMG caliber rifles, and magazines that can hold more than ten rounds of ammunition may not be sold in California. Possession of automatic firearms, and of short-barreled shotguns and rifles, is generally prohibited.