Basis to Determine Capital Gains

[Darren Preuninger]

My mother owns a working farm in North Texas that she inherited in the late 90s. She is considering selling a portion of the property for another investment that would not be a candidate for a 1031 exchange. My question pertains to how the IRS allows for the basis calculation for capital gains tax.

Would she have to prorate the basis for the portion she sells or would she be allowed to claim the entire basis now making the remaining property she retains entirety subject to future capital gains tax?

For example and to keep the math simple lets say the basis for the entire property was 1 million and she has made no improvements over time. She wants to sell half now for 1 million. 

Could she claim the entire basis with this transaction, make the remaining half she retains entirely subject to future capital gains, and pay no tax now?

Or would she only be allowed to claim $500k as the basis now making her subject to capital gains on the $500k profit?