There is no inheritance taxes neither in the US nor in New Mexico.
The federal estate taxes - that are paid by the estate and no by beneficiaries - applied to estates with values above $2,000,000 in 2008 (above $3,500,000 in 2009). New Mexico does not impose an estate tax after Jan. 1, 2005. So - if that the only property part of the estate - no estate tax will due. Your basis in the property will be the fair market value o the property on the date the decedent died - so if you sell shortly after - there will not be any capital gain taxes.
However if you inherit the property in 2010 - estate taxes are eliminated, but you will recognize the capital gain on that inheritance. Your basis will be the same as your father has - a fair market of the property at the time your father inherited the farm in 1950 and the difference between the basis and the sale price would be your capital gain.
In 2011 the estate taxes will be back, but it is expected that Congress will change the law by that time.
Unfortunately - that is a situation with estate taxes today... I wish your parents will live longer...
Since 2003, after the Congress passed a new estate tax law - the top tax rate was reduced from 55% to 45%(current level) and exclusion amount was increased from $600,000 to $2,000,000 in 2007-2008 and $3,500,000 in 2009. Most states followed the same way and eliminated state estate taxes (with some exemptions)
While most experts expect that Congress will change the tax law before then - if the Congress makes no changes - in 2011 the estate tax will return at a top rate of 55% and exclusion amount will be back to $600,000.
If the estate tax would be eliminated, then in order to justify the stepped-up basis for beneficiaries - unrealized capital gains would be subject to capital gains tax. Similar taxation model is implemented - for instance - in Canada. There are some exemptions - though - for instance inherited property that is a primary residence for the beneficiary is not subject for capital gains. However as the tax law that regulated this subject is not in effect yet - the list of exemptions is not finalized and we do not have any practical examples or court ruling this matter.