If it hasn't yet popped up on your Facebook feed, the bulk of the message goes like this:
"The Morton County Sheriff's Department has been using Facebook check-ins to find out who is at Standing Rock in order to target them in attempts to disrupt the prayer camps. SO Water Protectors are calling on EVERYONE to check-in at Standing Rock, ND to overwhelm and confuse them. This is concrete action that can protect people putting their bodies and well-beings on the line that we can do without leaving our homes. Will you join me in Standing Rock?"
The rest of the message instructs supporters to publicly check in at Standing Rock, then make a separate, private post visible only to friends in order to clarify what they are doing. As Snopes points out, however, the core of that statement is simply not true. Not only is the Morton County Sheriff's Department not monitoring Facebook check-ins, but even if they were, the remote check-ins "would not confuse or overwhelm them." On a technical level, trying to throw off law enforcement with a remote check-in is pointless. The Sheriff's Department re-iterated their position in a Facebook post stating "This claim/rumor is absolutely false."
In its own Facebook message response, the Sacred Stone Camp clarified that the Facebook message "did not originate from the Sacred Stone Camp FB page." The group claims "there is no doubt" that law enforcement monitors social media activity, but the check-ins help their cause only by bringing a bit of viral awareness. Although the group says they appreciate the show of solidarity, it would do much more to help their cause if all of those thousands of people "take physical action" in the form of a contribution to the group's legal defense fund, by joining up on their solidarity page or by actually coming down to protest in person – not just through a meaningless online check-in.
Curiously, TechCrunch points out that "Standing Rock" is still not a trending topic on Facebook, despite all the chatter. So, for all the well-meaning misinformation, the protest still has much less awareness -- or is less important in the eyes of Facebook's algorithms -- than fake news or Kylie Jenner and Tyga's Halloween costumes.