TL; DR Summary

• The Seattle Post Intelligencer says the Republican Platform calls to “Sell off public lands in the West, log national forests”.
• This link was widely distributed on social media.
• Snopes.com says the erroneous story was based on an incorrect blog post from ThinkProgress claiming the GOP plans to close national parks, monuments, wilderness areas, national forests, BLM lands  and sell them to private interests.
• Snopes.com notes the assertions about national parks, etc, are not supportable and that the Seattle PI actually quoted the 2012 platform, not 2016.  Read the link for their full analysis.
• The final 2016 Republican platform does call for a review of federal lands with a goal of turning over “certain” lands to states.

The basic propaganda method used here is the strawman argument. In the strawman argument, you create a fictitious statement from your opponent (in this case by exaggerating what they said) and then argue against that fictitious statement, rather than what the opponent actually said or promoted.

This argument relies on making assertions that many in the target audience are likely to believe as true (even though the assertions may be false). This approach works due to pre-propaganda that has “educated” your target as to the behavior and interests of the opponent (whether true or not). Due to social media’s friction-less propaganda vector, few question their “friends” when such items are posted (if they do, they may become unfriended or unfollowed),  where “Like” and “Share” are equivalent, and the lack of a “Like” suggests you support the strawman argument, unlike your “Friends”. Therefore, you shall not question but must instead signal  your virtue by clicking “Like”.
Basically, social media makes people dumber.
This particular item works as propaganda because it sounds plausible on multiple levels – including that it seems related (or in propaganda terms, is transferred) to the Bundy’s occupation of BLM lands in Nevada and Oregon, the Republicans favor privatizing some government functions and lands, and some western states have sought greater control over Federal lands (in several western states, the Federal government owns the majority of the land).
The original Think Progress blog post ties together an untrue headline with a photo of Cliven Bundy:

The linkage of the incorrect story title to the Bundy’s is, of course, an intentional way of transferring dislike of the Bundy’s to the Republican party. Transference is a standard propaganda method that associates one or more actors or objects with a goal of linking one’s feelings for one to the others.
The final draft of the 2016 Republic platform is available here.  The lower right of page 21 is the final wording of the relevant sections, per the above. The platform calls for the establishment of  a review process: “Congress shall immediately pass universal legislation providing for a timely and orderly mechanism requiring the federal government to convey certain federally controlled public lands to states.”
Thus, it is true that the Republican platform calls for a reduction in federally controlled public lands; however, the platform does not call for the sale of national parks, wilderness areas or national forests. A standard technique of propagandists is to exaggerate – exaggeration can then be used with strawman arguments, fear and other common propaganda techniques.