Where do you live in CA? If you live in SoCal, be pretty specific.

My general thought is that fixing your current soil is much better than bringing in the unknowns of new topsoil. The simple secret cure for bad soil is to use organic fertilizer. Beyond any chemistry shortcomings (curable with a soil test), most soils have had their organic content depleted with years upon years of chemical fertilizers without ever once applying organic fertilizer. The microbes (beneficial bacteria, fungi, protozoa, microarthropods, and other tiny critters) which cause healthy soil must be fed with real food at least occasionally to keep your soil fresh and healthy. Organic fertilizer is that food.

If you look at the ingredients of the good organic fertilizers you will see that they mimic the ingredients in dry dog and cat food. It is real food. You can simplify your life and save a lot of money by buying the raw materials and applying that directly to your soil. Buy according to what ingredients are inexpensive this year. Back in the early 2000s, corn was cheap at $3 per bag. Nowadays the best deal is alfalfa pellets (rabbit food) at around $12 per bag. The application rate is 20 pounds per 1,000 square feet. Use it once at that rate and in 3 weeks you can reapply at any rate up to 50 pounds per 1,000 square feet. With organics the more you use the better it works; however, if you dump a lot down on depleted soil, the organics will tend to stink as it decomposes. Work your way up to heavier doses. Also with organics you can apply any day of the year without fear of burning or overstressing the grass.

So, where do you live?