Government buildings and school zones are a no-go unless you have a license pursuant to PC 12050
The only 'group gatherings' that I can think of which are a no-go is something along the lines of picketing. I can't find the statute at the moment...
An the only time picketing is an issue is if it has to do with a strike, or other refusal to work.
If you are at a demonstration picketing against police brutality, or global warming, or people wearing fur coats, you can carry, provided you are otherwise legally carrying.
12590. (a) Any person who does any of the following acts while engaged in picketing, or other informational activities in a public place relating to a concerted refusal to work,
is guilty of a misdemeanor:
(1) Carries concealed upon his person or within any vehicle which is under his or her control or direction any pistol, revolver, or other firearm capable of being concealed upon the person.
(2) Carries a loaded firearm upon his or her person or within any vehicle which is under his or her control or direction.
(3) Carries a deadly weapon.
(4) Wears the uniform of a peace officer, whether or not the person is a peace officer.
(b) This section shall not be construed to authorize or ratify any picketing or other informational activities not otherwise authorized by law.
(c) Section 12027 shall not be construed to authorize any conduct described in paragraph (1) of subdivision (a), nor shall subdivision (b) of Section 12031 be construed to authorize any conduct described in paragraph (2) of subdivision (a).