Capital Gains Easement Act of 2013 - Amends the Internal Revenue Code to exclude from gross income, for income tax purposes, any gain from the sale or grant of a qualified real property interest to a tax-exempt organization made exclusively for conservation purposes. Defines "qualified real property interest" as any interest in real property which is: (1) the entire interest of the taxpayer, (2) a remainder interest, or (3) a restriction (granted in perpetuity) on the use which may be made of the real property. Exempts such a sale or grant of a qualified real property interest from the application of estate tax property valuation rules.