Although my Hacker Newsletter stats could be completely different than HN, it is a subset of HN users so it might be relevant - California averages around 20% of my opens and the USA about 70% of the total.

Edit: Just to add to this - New York and Massachusetts are the next highest and combined make up about the same as California.

Yes and when somebody in France makes a French equivalent of Le Hacker News, and a bunch of Americans start posting there, in second language French, then the "host country" readers can make the same geo assumption in reverse. ;)

25% of a website's userbase being located in one state of one country is a "vast majority" on the Internet, it having a far higher HN'er/population ratio then any other state or country.

To be pedantic, the definition of majority is half the group, and 'vast' implies upwards of 70%.

You probably mean something like a "large plurality"