Did California enter the US as a free state or slave?

It was admitted to the Union as free soil.

To get the South to agree to this, Congress had to make concessions, including the Fugitive Slave Act, which turned many Notherners towards Abolitionism, and pushed the country closer to civil war.

If California could have been admitted as two different states, divided along the line of the Missouri Compromise, war could have been avoided.