These tablets have roughly hewn granite bases with bronze plaques attached to them, angled forward for easy viewing. Each tablet explains the movements of the Confederate Army of Northern Virginia during the Gettysburg Campaign. Once upon a time and many years ago, they were all removed for safety reasons. During the early years of park management, selected commemorative elements were removed from the battlefield landscape for purposes of traffic flow and safety for park visitors. In recent years, the National Park Service realized the necessity for replacing these historic elements in the park and based on the 1999 General Management Plan, many of the signs and tablets removed during the 1930's and 1940's have since been restored to the park tour route. The most recent project was the rehabilitation and placement of the Itinerary Tablets for the "Army of Northern Virginia", completed in the summer of 2006. (National Par Service - Citation Below). Because of these tablets notable absence, they have been left off the contributing structures list, but in time, I am sure they will be added.
As already stated there are 10 markers located here along Seminary Ridge. If you are traveling south along West Confederate Drive (near the Schultz House), these monuments will be on the right or west side of the road; the monuments face the east, in the direction the Rebel troops attacked the Union lines 3/4 of a mile away to the east, located along Cemetery Ridge. The earliest date is the far right (northern) marker (June 26th), and the latest date is the far left (southern) marker (July 5th); this perspective would be if you were facing the tablets or looking west. The northern most tablet is the first tablet (chronologically) on the right, again if you are traveling south along the avenue. This waymark is for the fifth tablet to the right if looking south. There is plenty of parking on the side of the road. I would recommend parking on the opposite side of the tablets so you don't interfere with anyone's photos. Do not park on anything green or the Park Police will ticket you. I visited these ten monuments on Saturday, March 10, 2012 @ 11:15 AM and was at an elevation of 573 feet, ASL.
While looking at my map of GoogleEarth, I noticed the vast majority (in the high ninety percents) of the Confederate Tablets, monuments, and memorials are south of these tablets. I suppose it makes sense then for these tablets to be the harbinger or forbearer of things to come. They more or less welcome the visitor, giving a broad stroke overview of what happened leading up to Gettysburg, as well as generally explaining the events and movements here as well. The brigade, battalion and battery tablets go into much more detail and fill in the obvious gaps left by the tablets.
I found this nice excerpt from the Marker Hunter site (citation below): The Army of Northern Virginia tablets cover the time span from June 26 to July 5, 1863 – ten all told. The narrative follows the last of the Confederate infantry crossing at Williamsport; the wide ranging columns around Franklin, Cumberland, York and Adams Counties, Pennsylvania; then the concentration of forces toward Gettysburg; and finally the withdrawal from the field. If the reader browses the tablets, note the text strictly covers the arrival of the divisions to the field. The itinerary tablets are just that, and are mostly concerned with the movement time line. For the details of the battle, the visitor must go to the respective unit tablets on the field (all of these having been waymarked by yours truly). As was the standard for all tablets at Gettysburg, these were placed to allow the carriage or car bound visitor to read, pulled to the side.
Several sources have the construction date or installation date (the two are different) as 1901. The very first reference I have found of these tablets ever having been made is in the Gettysburg Commission's annual report of 1902. Before this date they were never mentioned so it seems the 1901 date may be accurate as the report talks about work done in the previous year of 1901. (I love detective work) The report says: Ten Confederate itinerary tablets, for which the inscriptions have been prepared, are now being cast and will be erected at a suitable point alongside of the Confederate avenue on Seminary Ridge. They will record the movements of the Confederate Army and its several corps, divisions, and brigades on each day from June 26, 1863, when the last of its forces crossed the Potomac into Maryland, until after the close of the battle and the retreat of the Confederates from Gettysburg, July 5, 1863. SOURCE.
The next year, the annual 1903 report of the Commission again mentions these tablet, only this time they are finished. The excerpt from that report reads: The ten Confederate itinerary tablets which were being cast at the date of our last report have since been finished and erected on the west side of the Confederate avenue on Seminary Ridge, near the junction of said avenue with the Fairfield road. They record the location and movements of the several corps, divisions, and brigades of the Confederate army on each and every day from June 26, 1863, when the last of its forces crossed the Potomac into Maryland, until after the close of the battle and the retreat of the Confederates from Gettysburg July 5, 1863. SOURCE For the record, these tablets were never mentioned in the 1901 report. That year however, West Confederate Avenue had just been finished.
There are hundreds of these types of non-sculpted monumentation for the various Confederate States & Union units which fought at Gettysburg, about 10 different variations of tablets, markers and monoliths by my reckoning. Six total designs represent brigade and these itinerant tablets (2), division (2), corps (2). Other designs include army headquarters (2), each different in a subtle way so as to distinguish between armies. Battalion/battery/advance position markers and regimental monuments for United States Regulars & Confederate have their own distinct design (2), bringing the total to ten designs at the battlefield. These bronze tablets were created by Albert Russell & Sons Co. of Newburyport, Massachusetts. The granite bases which accompany these tablets were created by the Van Amringe Company out of Boston, Massachusetts. The 1910 Gettysburg Commission report lists the awarded contracts to these companies for the tablets. All of these tablets were designed by architect Colonel Emmor Bradley Cope (July 23, 1834 - May 28, 1927). He designed pretty much every tablet for both the Union and Confederate armies, each one distinct, with several different varieties. He is buried in Evergreen Cemetery 
in Gettysburg, as well as he should be as this park and most of the things seen here today were designed by him and as such, are his legacy. These monuments/tablets were erected just after the turn of the century during the first and beginning of the second decade of the 20th century. Each one has since been preserved or restored at least twice since the turn of the 21st century. The plaques and tablets were erected by the Gettysburg Park Commission (established by the War Department). The Gettysburg Park Commission is also referred to as the Gettysburg National Military Park Commission or the Gettysburg National Park Commission, to clear up any confusions, especially my own.
On October 1, 1898, the Gettysburg National Park Commission in a letter to the Secretary of War set gave recommendations for continuing the task of organizing and progressing the work of the Gettysburg National Military Park. Every November they wrote their annual report which outlined the work of the GNPC for that year. The following is an excerpt from that report relevant to this waymark. The link at the end of the paragraph will take you to the entire report. The method of marking the positions of troops on this field, as approved by the War Department, is to place the principal tablet or monument of each command at the position occupied by the command in the main line of battle, and to mark the several important positions subsequently reached by each command in the course of the battle by subordinate and ancillary tablets, with appropriate brief inscriptions giving interesting details and occurrences and noting the day and hour as nearly as possible. SOURCE
Most of the Commission reports have been digitized and can be found HERE. The initial 1893 report up to and including 1921 can be found here. 1922 to 1926 are missing and have yet to be discovered. The years 1927 to 1933 were discovered in 1996 and are also included. To my knowledge this is the most comprehensive list of documents that illustrated the development and formation of the park.
and finally, the inscription on the monument, which reads:
Heth's Division Hill's Corps at Cashtown. Pettigrew's Brigade Heth's Division marched nearly to Gettysburg but was recalled. Pender's Division Hill's Corps marched from Fayetteville to Cashtown. Anderson's Division Hill's Corps remained at Fayetteville.
Rodes's Division Ewell's Corps marched from Carlisle via Petersburg to Heidlersburg. Johnson's Division Ewell's Corps marched from Greenville to Scotland Penna. Early's Division Ewell's Corps returned from York via Weiglestown and East Berlin and encamped three miles from Heidlersburg.
Pickett's Division Longstreet's Corps remained at Chambersburg guarding wagon trains. McLaws's and Hood's Divisions Longstreet's Corps marched from there to Fayetteville except Law's Brigade which was sent to New Guilford.
Stuart's Cavalry Division marched from Union Mills MD. via Hanover to Jefferson and had a fight at Hanover Penna. with Kilpatrick's Third Cavalry Division.
My Sources
1.
National Park Service
2.
Gettysburg Commission Field Reports (1903)
3.
Gettysburg Daily
4.
Stone Sentinels
5.
Historical Marker Database
6.
Marker Hunter
7.
Draw the Sword