" this section are subject to,???(a) the terms of any gift, endowment, or trust relating to, and the rights of any holders of mortgages or other securities over, residual Crown land or any improvements on any such land:(b) any other enactment or rule of law that must be complied with before any residual Crown land is disposed of:(c) any feature of the title to any residual Crown land which prevents" . . . . .