They're referring to California's statewide referendum system so the answer would be "all of California".

well he's making it sound like a bad thing, so I wanted to know what exactly he meant.

Probably the part where we can amend our state constitution with 50% + 1 on ballot initiatives.

Prop 8, for example.

Or Prop 13.

Prop 8, officially titled Proposition 8 - Eliminates Right of Same-Sex Couples to Marry, was a statewide ballot proposition in California. On November 4, 2008, voters approved the measure and made same-sex marriage illegal in California.

On June 6th, 1978, nearly two-thirds of California's voters passed Proposition 13, reducing property tax rates on homes, businesses and farms by about 57%. The Environment Prior to Proposition 13. Prior to Proposition 13, the property tax rate throughout California averaged a little less than 3% of market value.

The interesting thing about Prop 8 is, a few years later, the outcome of the vote has been totally reversed, same-sex marriage is the law of the land, and it now has solid majority support. The will of the people can change in a short time. You could imagine a similar outcome for the Brexit vote, if it weren't such a permanent change.

The most salient and controversial facet to Prop 13 wasn't the immediate rate change, but the cap on increases when a property was continuously owned.

To me worst part wasn't the cap itself - I think it's fair for residential properties, but that it was also applied to commercial properties.

(for context to the unaware, these are generally regarded as terrible policies)

"generally"

Probably Marin.