I have my Philippine Driver's License when I came here in US. The California Driver's Manual states that a foreign driver's license can be used here in CA as long as it is still valid. The bearer is called a visitor driver. Since I am no longer a visitor, I need to get a CA DL. It is an advantage if you have a license already from your country because you don't have to pay $$$ for the driving lessons. I paid $27 (not sure cos I forgot) for the DL application and just take the written and manuat test anytime. Right now, I am preparing for my written exam. It has been postponed always because I don't have time or just being lazy to set a time for it. But I am planning to get my CA DL this month since I badly need to drive myself to the school, office and home. Hubby doesn't have much time to drive and pick me up. Also, my Phi DL is expiring this March. If ever I get a driver's license this month, it will expire right away this August because my Green Card will expire too. I can renew it right away without having my DL suspended if I apply for a removal of conditions for my green card ahead of time (90 days before the expiration date). In that way, I can have my NOA (Notice of Action) from USCIS that I can submit to DMV in order for me to go on with the DL renewal. This is based on my friend's experience.
More info at DMV.CA.GOV