In 1780, the secretary of the French legation in Philadelphia, Francois Marbois, submitted to various members of the Continental Congress a list of questions concerning the thirteen American states. Joseph Jones, a member of the Virginia delegation, believed Jefferson the most capable person to answer these queries for the state of Virginia and put Marbois's questionnaire in his hands. The answers composed by Jefferson to twenty-three queries make up his Notes on the State of Virginia, which has been called the "most important scientific and political book written by an American before 1785." Among the queries submitted by Marbois was one asking for a description of the Indians in the state (Query XI). Jefferson long had an interest in the Indian population of his native Virginia and his response to Query XI constitutes an impressive description of Indian tribes, their number, history and geographical location, as well as their languages. As part of this response, Jefferson describes in detail his exploration of an Indian burial mound in the "neighbourhood" of Monticello. He states it was "situated on the low grounds of the Rivanna, about two miles above its principal fork, and opposite to some hills, on which had been an Indian town." 
Jefferson and others were aware of "many" barrows, as he called them, in the area . This particular mound or barrow was known locally as "the Indian Grave"  and he excavated it in order to ascertain which of several views of the Indian burial customs was correct: "That they were repositories of the dead, has been obvious to all: but on what particular occasion constructed, was matter of doubt. Some have thought they covered the bones of those who have fallen in battles fought on the spot of interment. Some ascribed them to the custom, said to prevail among the Indians, of collecting, at certain periods, the bones of all their dead, wheresoever deposited at the time of death. Others again supposed them the general sepulchres for towns, conjectured to have been on or near the grounds; and this opinion was supported by the quality of the lands in which they are found, (those constructed of earth being generally in the softest and most fertile meadow-grounds on river sides) and by a tradition, said to be handed down from the Aboriginal Indians, that, when they settled in a town, the first person who died was placed erect, and earth put around him, so as to cover and support him; that, when another dies, a narrow passage was dug to the first, the second reclined against him, and the cover of earth replaced, and so on."
Jefferson wrote that the mound was "of spheroidical form, of about 40 feet diameter at the base, and had been of about twelve feet altitude...I first dug superficially in several parts of it, and came to collections of human bones, at different depths, from six inches to three feet below the surface.These were lying in the utmost confusion, some vertical, some oblique, some horizontal, and directed to every point of the compass, entangled, and held together in clusters by the earth...to give the idea of bones emptied promiscuously from a bag or basket, and covered over with earth, without any attention to their order."
Jefferson proceeded to "make a perpendicular cut through the body of the barrow, that I might examine its internal structure. This passed about three feet from its center, was opened to the former surface of the earth, and was wide enough for a man to walk through and examine its sides." He observed several strata of bones with those nearest the surface the least decayed and "conjectured that in this barrow might have been a thousand skeletons." There was no evidence of violence to the bones such as holes made from bullets or arrows. The latter finding argued against the view that the remains in the mounds were of warriors killed in battle; nor did Jefferson find that the bodies had been placed upright as others had speculated based on local Indian lore.
Jefferson adds that "about thirty years ago" he observed a party of Indians to visit the barrow. "[They] went through the woods directly to it, without any instructions or enquiry, and having staid about it some time, with expressions which were construed to be those of sorrow, they returned to the high road, which thay had left about a dozen miles to pay this visit, and pursued their journey." Jefferson submitted a draft of the Notes to Marbois in 1781, and it has been suggested that Jefferson's sighting of the Indians at the barrow "about thirty years ago" would have been, therefore, when he was about 8 years old. However, this estimate, given Jefferson was born in 1743, is valid only if the passage was included in the Marbois draft and not added to a later copy, and, of course, that Jefferson remembered accurately the number of years past. The original manuscript delivered to Marbois in 1781 has never been found and may no longer exist, and it is known that Jefferson continued work on the 1781 manuscript over the next few years. 
Jefferson did not record exactly when he made his excavation of the Indian mound, and numerous dates have been suggested:
Holland says "about 1780" ; Bedini suggests it was "around 1782"  but may have been undertaken in the 1770s. Marie Kimball argues that Jefferson's "observations were, in all probability, made before 1773, the year Jefferson began to become so involved in the Revolutionary movement that he had little thought or time for anything else." The Monticello and Jamestown archaeologist, William Kelso, writes: "It is certain that Jefferson, at some time in his twenties, organized an archaeological expedition to that mound, directed archaeological fieldwork, analyzed what he found, and published his conclusions." Thus Kelso, too, believed the excavation likely to have taken place before 1773.
Evidence presented by Wilson, however, makes a strong case for the summer or early fall of 1783. As part of his investigation into the evolution of the Notes, Wilson points out that Jefferson's account of the dig was a primary addition to the draft he completed in the summer or early fall of 1783. Since Jefferson left Virginia for Philadelphia on the 16th of October of that year, Wilson argues that the dig was made between the completion of the draft and his departure to Philadelphia. Moreover, based on an analysis of Charles Thomson's comments made in the spring of 1784, Wilson suggests that Thomson had not seen a first-hand account of the dig as it appears in the later draft and that "Jefferson was prompted to describe his dig, many months after the dig itself by Thomson's spring 1784 commentary." 
Thomas Jefferson: Father of American Archaeology
Archaeological studies have identified thirteen mounds in the Piedmont, Ridge, and Valley regions of central Virginia, including that described by Jefferson. These burial mounds date to the late prehistoric and early contact era (ca. AD 900-1700), vary in size and composition (e.g., earth-stone and conical), may contain the bones of more than a thousand individuals, and, interestingly, these collective burial mounds typically are bereft of artifacts .
The site of Jefferson's mound is on the right (south) bank of the South Fork of the Rivanna River just north of Charlottesville and has been explored by archaeologists on several occasions, most recently by members of the Anthropology Department of the University of Virginia . However, as early as 1911, Bushnell explored the area and reported that the mound had "entirely disappeared," most likely washed away due to flooding in the lowland where Jefferson found it. On the other hand, scientists agree that the "Indian Town" mentioned by Jefferson was the Monacan village of Monasukapanough, which probably occupied both banks of the South Fork at this point  and research at this site is ongoing.
The original territory of the Monacan Indians and their allies once "comprised more than half the state of Virginia, including almost all of the Piedmont region and parts of the Blue Ridge Mountains;" these indigenous people were mound builders, placing the remains of their dead over time in sacred earthen graves.  Charles Thomson gave an eyewitness account of these burial rituals as part of his extensive comments on a draft of Jefferson's Notes, which Jefferson included as an appendix to the Notes.
Jefferson's excavation of the Indian mound earned him the title of "Father of American Archaeology" and "first American archaeologist". His systematic trenching and use of stratigraphy (i.e., stratigraphic observation) as part of his exploration of the Indian mound, "anticipates the fundamental approach and the methods of modern archaeology by about a full century."
- Gene Zechmeister, Monticello Research Report, November 2010
Notes, ed. Peden. Peden's Introduction to this edited volume of Jefferson's Notes is the source for much of the background material in this section.
 William M. Kelso, Archaeology at Monticello, (Charlottesville, Va.: Thomas Jefferson Memorial Foundation, 1997), 15.
 Douglas L. Wilson, "The Evolution of Jefferson's 'Notes on the State of Virginia,'" VMHB 112 (2004): 98-133. Examination of the manuscript held by the Massachusetts Historical Society, which is considered to be the setting copy for the 1785 Paris edition (http://www.masshist.org/thomasjeffersonpapers/notes) reveals that the passage of interest was part of the fair copy and not an addition, unlike the passage describing Jefferson's excavation of the mound. The description of Jefferson's sighting of Indians visiting the barrow may well have been included in the Marbois draft given Wilson's statement that "it seems likely that the answers supplied to Marbois, while no doubt ripe with Jefferson's extensive personal knowledge and impressions, were not the result of extensive research" (105,108). In other words, it is certainly plausible that Jefferson included in the copy to Marbois the passage based on his "personal knowledge" of Indians visiting the mound.
 C. G. Holland, "Albemarle County Settlements: A Piedmont Model?," Archaeology Society of Virginia Bulletin 33 (1978): 229.
 Silvio A. Bedini, Jefferson and Science, (Charlottesville, VA: Thomas Jefferson Foundation, 2002), 51.
 Jeffrey L. Hantman, Karenne Wood, and Diane Shields, "Writing Collbaborative History: How the Monacan Nation and archaeologists worked together to enrich our understanding of Virginia's native people," Archaeology 53 (2000): 56-59.
 Karenne Wood, "Monacan Indian Nation," in The Virginia Indian Trail (3rd. ed.), ed. Karenne Wood (Charlottesville, Va.:Virginia Foundation for the Humanities, 2009), 36.
 Karl Lehmann-Hartlebe, "Thomas Jefferson, Archaeologist," American Journal of Archaeology 47 (1943): 161. See also William H. Stiebing Jr., "Who First Excavated Stratigraphically?", Biblical Archaeology Review, January/February (1981): 52-53.