Legal Question in Wills and Trusts in California

The joint tenancy is severed because the joint tenants no longer own the property. It is now owned by the trust. If it is a typical intervivos trust, the transfer is of almost no consequence to the rights of posession, occupancy, etc., but it is a change in the owner of fee title and that severs the joint tenancy. And you are mistaken that a sale would not sever the joint tenancy. A sale and a transfer to the trust are the same, a change in the owner of the fee simple estate. The other things you list do not change ownership of the fee simple estate (although a life estate might depending on how it was structured and granted).

Timothy is spot on- there has been a severance of the "unities" giving rise to the original joint tenancy.