Elise found more information on the Buried Poems from this dated website:
"LOCATION: places such as an unnamed, uninhabited island in the Florida Keys, Arches National Monument Desert in Utah, and at the bottom of the Highlands of Navesink near Sandy Hook, New Jersey.
"Holt gave five people (Michael Heizer, Philip Leider, Carl Andre, John Perrault, and Robert Smithson) a packet of information which allowed them to find and dig up a poem. Each poem was buried in a location which was chosen based on their personality. Included in the packet were such items as maps, photos, very detailed directions for finding the poem, along with either postcards, cut out images, and maybe specimens of leaves or rocks from the site. The recipient would eventually understand his connection with the site. The poems were all buried in vacuum containers which would last long enough for them to dig it up whenever they happened to be near the area."
Of course I would like to know if any of these people ever found their poems - the idea of them sealed in vacuum containers is intriguing though anti-ephemeral just like the vast majority of American Land Art.
My search for more information brought me to Jan Estep's Beneath the Surface of Language. Estep spent two weeks at the Center for Land Use Interpretation residency program to create "a site-specific map/text/photo project featuring the 54-mile backcountry Silver Island Mountain Byway, a BLM-managed route near the Bonneville Speedway just outside of Wendover, Utah."
She comments on Nancy Holt's Buried Poems and John Baldessari's California Map Project - two of my favorite works in the genre of art and mapmaking.
See more of Estep's work here. Image above from Estep's Site #2.