26 CFR 1.167(i)-1: (i)-1 Depreciation of improvements in the case of mines, etc.

Property used in the trade or business or held for the production of income which is subject to the allowance for depreciation provided in section 611 shall be treated for all purposes of the Code as if it were property subject to the allowance for depreciation under section 167. The preceding sentence shall not limit the allowance for depreciation otherwise allowable under section 611.