Can I drive with a European driver's license in California?

From personal experience, most country's drivers licenses work without any ado. I have been laughed at for showing an international license, even though that is formally the correct approach.

Be aware that they rent hundreds of cars every day to Germans, French, British, etc. citizens, and not a quarter of them bother to prepare in any way.

However, there is no guarantee- the formal correct way is the international license, even though it might end being a waste of time and money.

I advise playing exactly by the rules defined by the rental companies. The experience of other renters cannot be relied on.

Use the published information of your proposed rental company. For example, from Hertz:

An acceptable, valid driver's license issued from your country of residence must be presented at the time of rental. The driver's license must be valid for the entire rental period. If the driver's license is in a language other than English, and the rental is in the United States, an International Driver's Permit is recommended. In all cases, a valid driver's license issued from your home country must be provided, whether or not you possess an International Driver's Permit. You will not be allowed to rent a Hertz vehicle with only an International Driver's Permit.

Note that there may be a requirement to produce an additional UK Licenses Summary document, which must be obtained by you from the UK licensing authorities website. Hertz do indicate that this is required by them only in a small number of countries, not including the USA. I have never been asked for it but I always obtain one before travel. Again check your renter's terms and conditions in case they do require it.

Similarly, even if most folks with (say) a French language license are not asked for the International Permit I would still get one. All you need to foul up your plans is an over-zealous employee.

I am not aware of any extra rental charges solely because of having a non-US license.