Like my Agronomy teacher used to say "Don't treat you soil like dirt!". Treat it with respect and appreciation for the amazing things it does for your garden. Sure, sometimes it can be hard and dry or sticky and wet, but with a little TLC it will be the reason you have a beautiful successful garden.
Valley soils vary widely by location. Most of the San Joaquin Valley has exceptional soil, which is why we can grow anything. The range of soil types goes from sandy to heavy clay or, worst of all, hardpan.
Sandy soils do not hold water or nutrients and need organic mulches to enrich them. This process needs to be done over several years to build up the soil quality. You can apply 3-5 yards of compost per 1,000 sq ft. Additional topdressing in summer will help reduce water loss. Use a slow release organic fertilizer to increase microbes that also help to improve your soil.
Heavy clay soils are the exact opposite of sandy ground. Clay soil is rich in nutrients that are tied to the clay particles and not available to plants. Drainage is often poor and the soil becomes very hard when dry. Adding organic mulch and compost will help "open" the soil by not allowing the clay particles to "stick" back together. Adding Gypsum creates a chemical reaction that induces clay particles to clump up which also improves drainage. A good product called John & Bob's Soil Activator has both gypsum and concentrated compost, plus microbes that help change soil texture and release nutrients. This greatly reduces the amount of compost needed per year.
Many people mistake very hard clay as true Hardpan. Hardpan is essentially a layer of rock that must be broken up by physical or mechanical means. It can be only inches thick to several feet. Either way, water will not percolate thru and roots will not work their way into it.
Now is an excellent time to mulch your soil, add gypsum or John & Bob's Activator. Don't delay. The more time compost products have to decompose the better your soil will be for spring planting. The rain will drive the mulch deeper and starts the composting process before spring planting.