The First CS Corps was also known as Longstreet’s Corps. The unit was commanded by General James Longstreet (January 8, 1821 – January 2, 1904) who was one of the foremost Confederate generals of the American Civil War and the principal subordinate to General Robert E. Lee, who called him his "Old War Horse." He served under Lee as a corps commander for many of the famous battles fought by the Army of Northern Virginia in the Eastern Theater, but also with Gen. Braxton Bragg in the Army of Tennessee in the Western Theater. Biographer and historian Jeffry D. Wert wrote that "Longstreet ... was the finest corps commander in the Army of Northern Virginia; in fact, he was arguably the best corps commander in the conflict on either side." Upon my multiple visits to this hallowed battlefield, it is his name I see the most other than Lincoln.
The Longstreet's Corps - CS Corps Tablet is Southwest of Gettysburg on West Confederate Avenue, close to the intersection of West Confederate Avenue and Millerstown Road, on the right when traveling south on West Confederate Avenue, near Pitzer's Woods, and located near stop six of the driving tour of Gettysburg National Military Park, just 472 feet north of the Longstreet Observation tower, which is on the opposite side of the road. The monument faces the east. 
Parking can be had at the observation tower. The last couple or so slots are for buses so don't park there. Please do not park on the grass, park on the side of the road if you are not using the lot. I cannot emphasize that enough! You will be ticketed. I visited this monument on Saturday, March 10, 2012 at 3:56 PM, just before the clocks were set ahead for the Spring. I was at a 579 foot ASL elevation.
The monument was erected in 1907, according to the NPS/NRHP narrative. Another source has it at December of 1906. It is simply amazing with all the work put into these monuments, not one person had the wherewithal or simple presence of mind to write down the dedication dates or manufacturing dates. I know for sure the work was done under the direction of the Gettysburg National Park Commission (established by the United States Department of War), after they took over the administration of the park from the Gettysburg Battlefield Memorial Association (whose funds had expired) on March 3, 1893, and whose stewardship was then transferred to the National Park Service in 1933, which entity still operates the park today) SOURCE.
Draw the Sword, with descriptive help from the NPS site, offers the following description: A rectangular granite monument, with a large bronze tablets thereon, describing the engagements and movements of each army corps. Rock-faced granite monolith, 4 feet 2 inches (close to it) wide by 2 feet wide (thick) by 7 feet high (this is my reckoning), with bronze narrative tablet mounted on obverse polished face. One of the Confederate army corps monuments, denoting the service of the First Corps, Army of Northern Virginia. Constructed by Albert Russell & Sons Co. of Newburyport, Massachusetts and erected by the United States War Department (well, not exactly accurate). The inscription on this tablet reads:
Army of Northern Virginia
First Army Corps Lieutenant General James Longstreet
McLaws's Division Major General Lafayete McLaws
Pickett's Division Major General George E. Pickett
Hood's Division Major General John B. Hood, Major General E.M. Law
Artillery Reserve Ten Batteries Colonel J.B. Watson
July 1. McLaws's Division encamped about four miles from Gettysburg a little after dark. Hood's Division reached the same distance about 12 p.m. Law's Brigade on picket at New Guilford. Pickett's Division guarding trains at Chambersburg.
July 2. Moved that portion of the Command which was up to gain the Emmitsburg Road on Union left. Delayed attack until 3:30 p.m. when Law's Brigade joined from New Guilford. McLaw's Division in position facing Union left. About 4 p.m. Hood's Division moved further to the right and took position partially enveloping Union left. The Batteries opened about 4 p.m. upon Union troops on Emmitsburg Road. Hood's Division pressing on left and McLaws's in front. The Union troops were dislodged. The engagement lasted until nearly night with heavy losses. The ground gained on the right was held. The left was withdrawn to first Union position at Peach Orchard.
July 3. Pickett's Division reached the field at 9 a.m. Pickett's Heth's and part of Pender's Division were ordered to form column of assault on Union centre on Cemetery Hill. The Batteries opened about 1 p.m. About 3 p.m. Pickett advanced in good order under a severe fire and was repulsed at the stone wall losing heavily. McLaws's and Hood's Divisions were not seriously engaged and after rectifying their lines remained on the field during the day and night.
July 4. The Corps took up the line of march during the night.
Casualties killed 910 wounded 4339 captured or missing 2290 Total 7539
There are scores of similar monuments for the various Confederate States & Union units which fought at Gettysburg. Four designs represent brigade, division, corps and army headquarters, and each has elements which identify it as Union or Confederate. Depending on who you talk to, there are nine different types of these tablets and monoliths here. Many of the tablets were created by Albert Russell & Sons Co. of Newburyport, Massachusetts and are made of granite, bronze and concrete, or some combination. All of these tablets were designed by architect E.B. Cope. He designed pretty much every tablet for both the Union and Confederate armies, each one distinct, with several different varieties. The monuments were erected just after the turn of the century during the first decade of the 20th century. Each one has since been preserved or restored at least twice since the turn of the 21st century. Curiously, this one has not according to the NPS page. Given its pristine condition, I'd say the Park Service needs to update its records. 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, 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
Information about these specific types of monuments:
CORPS HEADQUARTERS MARKERS (FOR UNION & CONFEDERATE TABLETS)
Corps headquarters are similar to division headquarters, consisting of a large, rectangular stone. The difference are the brass tablets set into the stone, which instead of being rectangular like the division tablets, instead have a curved-and-scrolled top, much more ornate and distinctive. I also found the Union Corps tablets to be higher and thicker then their Rebel counterparts.
The union tablets are kind of neat, each individual one having a corps or service branch symbol like the diamond of the Third Corps, the Maltese Cross of the Fifth Corps or my personal favorite, the Trefoil for the Second Corps. There can also be found a full moon, a crescent moon, a cross, and a star.
The three Confederate monuments are not so bedazzled with symbols, rather, at the top they just have written on bronze tablet, Army of Northern Virginia. There are only three of the Rebel monoliths compared to nine of the Union Corps headquarters markers. One of the nine is for the entire Artillery Reserve so technically there are 8 Corps represented at Gettysburg or 9 depending to whom you speak.
At Gettysburg, to understand the order of battle and how men were arranged, simply understand the logic and system behind the monuments. Sometimes however, there are weird exceptions which break the pattern and are confusing and make no sense. When I visited the Peach Orchard (another battlefield found here) I found three monoliths fashioned in the distinctive Corps design but upon closer inspection I found them to be not for the Union Corps but for the 1st & 2nd Divisions of the 3rd Corps (as well as the one for the entire Artillery Reserve which I can excuse).
There are four of these tablets at the beginning of the orchard, all lined up in a neat row. The only reason I can think for the being constructed in the same way and manner as the Corps tablet was to provide uniformity. The Division tablets are the Birney's Division - US Division Tablet, 1st Division, Third Corps, the Humphreys' US Division Tablet, 2nd Division, Third Corps, the Randolph’s Artillery Reserve - US Division Tablet and the only authentic one, the Army of Potomac, 3rd Corps Tablet. Click the hot links provided to review those waymarks so as to have a clearer understanding. SOURCE & SOURCE
The Longstreet's Corps - CS Corps Tablet is a contributing feature to the Gettysburg National Military Park Historic District which is nationally significant under NR Criteria A, B, C & D. Areas of Significance: Military, Politics/Government, Landscape Architecture, Conservation, Archeology-Historic. Period of Significance: 1863-1938. The original National Register Nomination was approved by the Keeper March 19, 1975. An update to this nomination was approved by the Keeper on January 23, 2004. The monument is identified as structure number MN460.
From the Nomination Form:
1 of 3 Corps Tablet in Park. Records movements & itinerary of Longstreet's 1 Corps during Battle of Gettysburg, July 1-3, 1863. Located W side of West Confederate Ave, S of intersection w/ Millerstown Rd.
Short Physical Description:
Rough-hewn monolith, 4'2"x2', 7' high. Bronze inscription tablet, 3'7"x4'1", mounted on polished E face of monolith.
Long Physical Description:
N/A
My Sources
1.
NRHP Nomination Form
2.
Stone Sentinels
3.
Virtual Gettysburg
4.
Draw the Sword
5.
Historical Marker Database
6.
Wikipedia