Furnished apartments are not the norm in CA, but you still can find them in area near universities. In Riverside County, they are near UCR (University of California Riverside).
You can also rent a unit in extended stay apartments. Extended stay lodgings are hotels, motels, or apartments building that cater to business people who need to stay in an area for more than one month. The cost is higher than regular apartments but it's fully furnished and you don't have to pay for utilities, cable TV, local phone calls, or internet. Refrigerator, air conditioner, kitchenette with pots, pan, dishes, and utensils, bed with linen, weekly cleaning and housekeeping, etc. are all included in the rent. All you have to bring is your clothing and nothing else so that may be a good fit to you.
Companies with staffs from outside of the state/country often have contracts with extended stay, so perhaps your employer can help you with that.
You can also share a house or large apartment with someone else. Most of them are fully furnished and your cost is much lower than living by yourself. Craigslist is also a good source for that, or your employer can set you up with someone in their existing staff.
You still can visit the rest of CA in road trip with your income.
From Riverside, you can take easy day trips (no hotel cost) to see the glitzy Beverly Hills, swim in the beaches in Orange County, watch dolphins in Sea World San Diego, go up on Aerial Tramway in Palm Springs, ski in Big Bear Mountain in San Bernardino County, etc.
Santa Barbara, the wine country in San Luis Obispo County, Big Sur, or Carmel-by-the-Sea can be done with one night stay in hotel. San Francisco is 450 miles or 7 hour drive so it doesn't cost much in gasoline either and you can do that over a long weekend with 2 night stay in AirBnB.
Las Vegas is only 250 miles or 3.5 hours in good traffic (weekends are different story). The best time to see Vegas is during the week when you don't have to fight with traffic from Southern CA, and when hotels offer good deals in room rate.
Assuming your salary if after tax and you live conservatively (not paying very high rent, not spending a lot of money in shopping or drinking in clubs), you can travel within CA without difficulty. We do that all the time and our retirement income for two people is lower than your salary for one.