Native Californians were pretty damn adaptable. From the time that people first entered the area around 11,000 to 12,000 years ago up until the Europeans showed up, the people here managed to find a way to live in nearly every environment that the large and varied state offers - from deserts to glaciers, from swamps to forests, from plains to mountains. These people were smart, made good use of the resources available, and arranged themselves socially and politically in ways that allowed them to take advantage of their neighbor's resources (sometimes by violence, but more typically by trade).
Given this, there is one big glaring hole in California's archaeological record: pottery.
Generally, by the time a society has developed a sedentary or semi-sedentary lifeway (living in villages, collecting and storing food, etc.) one can expect to see pottery as part of the toolkit. Not so in much of California.
Pottery is a remarkably useful thing. It allows the creation of vessels of the exact size and shape that you need, which are relatively lightweight, and relatively durable - plus, if it breaks, you can create another identical one. Pottery can be made and sealed to be resistant to rodents, protect foods from the elements, and even mark who owns the contents of the pottery. Really, considering all that it can do, who wouldn't want pottery?
Well, apparently, the Native Californians.
I don't want to over-generalize. There were some groups in California - especially in the eastern Sierra Nevada and the Mojave Desert, who did make and use pottery, and pottery began to appear in the archaeological record of San Diego County late in prehistory. Also, some pottery from the peoples of the Great Basin (which covers most of Nevada and Utah) showed up in California, presumably brought by extensive trade networks. But for most of California there was little pottery until the Spanish showed up. Which is just kinda' weird.
So, given that pottery is useful and that it shows up all over the world, and that it likely would have been nice for the Californians to have it, you have to wonder why they didn't set about making it. Most of the usual explanations for why a technology didn't develop in a region don't wash:
They lacked the raw materials. Suitable clay and temper material are present throughout the state.
They didn't know how to do it. Baked clay balls* are found in San Joaquin Delta sites, indicating that the principle of "heat clay up, get rock-like material" was known, and there are other, rare, examples of locally-made ceramics in other parts of California, so the basic technique was known. Also, ceramic manufacture was independently invented at different places and time the world over, so even if there wasn't supporting evidence for the people comprehending the basic concept, why would California be any different from anywhere else?**
They didn't need it. Well, this one is kind of true. The Native Californians made extensive use of basketry to serve many of the functions that pottery normally serves. The thing of it is, though, that while the baskets are fine (or even ideal) for many of these functions, pottery is better for some of them (such as making storage containers that keep rodents out). Also, while they may not have manufactured ceramics, many people did make use of carved stone bowls and pots to serve the functions that ceramics would normally have served, and these stone vessels were considerably harder to manufacture.
We could keep going, but the simple fact of the matter is that we haven't quite developed a good reason for the Native Californians to have not made more extensive use of pottery. There must have been a good reason, we just don't know what it is. The answer may be complex, dealing with social mores and a need to keep all members of society gainfully employed (which may mean not bringing in a new technology that could replace an old one), or it could be as simple as a general lack of interest due to the development of compensating types of basketry and stone vessels.
Regardless, the lack of pottery is both curious and interesting.
*These are cool artifacts. One of the most common ways for native Californians to cook the seed gruels that were important parts of their diets was to put the gruel into a water-tight basket and toss heated rocks into the basket in order to cook it from within. Well, the San Joaquin Delta is prone to flooding, and so fine sediments covered most of the locally available rocks. In response, the people living here made their own heating rocks by making little balls of pottery.
**An offshoot of this one is: They lacked the aptitude to develop the techniques for making pottery. I have never heard this one from an anthropologist, but I have heard it from members of the public. And really, it's about as stupid, ignorant, and bigoted a statement as you could cook up. It's essentially saying "they weren't smart enough to figure it out." Look at the previous paragraph, the one that starts with "*", they not only could, but did figure it out. These were smart people, good at observing their surroundings, otherwise they would not have been as succesful ins preading across the land as they were. But, hey, if you think you're so much smarter, we'll dump your ass down in the middle of the Sierra Nevada, naked and with nothing but a pound of obsidian, and then we'll take bets on how long you'll last.