The "concealed dirk or dagger" laws of California are a little complicated. First, any fixed-blade that is "capable of ready use as a stabbing weapon" is defined under California law as a "dirk or dagger" (CA penal code 16470), regardless of it's design or number of edges. Technically, a fixed-blade is not considered "concealed" just because it's carried in a pocket.
The California penal code does specify that carrying a fixed-blade openly in a sheath suspended from the waist is not to be considered a "concealed dirk or dagger" (CA penal code 20200), but that is not the only manner of fixed-blade carry that is legal.
Here's where it gets complicated- just because a fixed-blade is concealed, it's not automatically a violation of the prohibition on concealed fixed-blades.
Superior court rulings in California have determined that the illegality of a concealed fixed-blade is to be determined by the intent of the person carrying the knife (as well as the knifes ability to be used as a "stabbing weapon"). If a prosecutor can demonstrate that a person was intentionally trying to conceal a fixed-blade, and if that person were convicted, that conviction would stand. However, the courts have determined that if a person were caught with a concealed fixed-blade, but they were not intentionally trying to conceal it, then they should not be charged, much less convicted, and such a conviction could be overturned.
The court described a few different scenarios to illustrate a persons lack of criminal intent when carrying a concealed fixed-blade, like for example- a person wrapping a fixed-blade kitchen knife in a paper towel and putting it in their pocket for use in food prep at a later time, and, a mechanic or other worker who puts a knife (or other item capable of use as a stabbing weapon) in their pocket and goes to lunch forgetting it's there, and, a person openly carrying a fixed-blade and the knife becomes temporarily covered by an article of clothing. The courts sought to provide legal protection from prosecution for people who were innocently carrying a concealed fixed-blade, but had no criminal intent in doing so.
If a person were carrying a fixed-blade in their pocket, and if it were not clearly identifiable as a fixed-blade (maybe only a small portion of the handle showing), and if it could be proven that it was the persons intent to conceal the knife, then they could be prosecuted, and if convicted, their conviction upheld on appeal.
To put it simply- if it's clear that a person was intentionally trying to conceal a fixed-blade from view, then they have broken the law.
Three of the cases, and case laws, I am referring to regarding the courts determination that the "intent" of a person defines whether or not a concealed knife is a criminal offense are- People of CA v. Rubalcava, People of CA v. Aubrey, and People of CA v. Oskins.
I forget in which case the court referenced an article of clothing accidentally covering an openly carried fixed-blade, but it's out there.