I have heard that a land grant is similar to a land patent in that the paper represents an offer of whatever is being granted (land in this case) and there has to be an "act" to accept the grant. Otherwise it is simply an offer hanging out there in space. In the case of the land patent it would appear that simply recording the paper is enough to indicate acceptance.
Here is what the state of Pennsylvania enacted to accept a grant from the U.S. in 1863:
http://www.libraries.psu.edu/speccol...n/palndgrt.htm
And here is one from a state that turns down land grants:
http://www.citizenreviewonline.org/july_2003/oregon.htm