Knife laws are complicated, but concealing fixed blades can be problematic in many more states than California: Wyoming, Wisconsin, West Virginia, even Kentucky, Pennsylvania, Oklahoma, Nevada, Mississippi, Maine, and Hawaii all have laws that could prevent the lawfulness of concealing any fixed blade. Because each state's laws are different, I can't possibly detail how all the prohibitions work, but one example could be a statute that prohibits the concealed carry of any "dangerous or deadly weapon." Then there can be case law that establishes that a steak-knife constitutes a dangerous weapon. In some states, the law is particularly onerous, while others you simply can't be assured whether that carrying that fixed blade is lawful or not.
There are many more states, including Florida that have specific length limits on concealed blades, some of which are as little as 2.5 inches (Chicago) or 3 inches (Delaware and Rhode Island). Some places you wouldn't necessarily expect too: Colorado prohibits concealing knives over 3.5 inches, which would include the common Morakniv.
I frequent several different states in the west and the thing that is lawful to carry in all of them is a folder, and there are no length limits in any of them. Several of them do not infringe on 2nd amendment rights with respect to knives, but there is more than one that does. I'm pretty sure it's worse in the east.