The high-water mark of the Confederacy refers to an area on Cemetery Ridge near Gettysburg, Pennsylvania, marking the farthest point reached by Confederate forces during Pickett's Charge on July 3, 1863. Similar to a high water mark of water, the term is a reference to arguably the Confederate Army's best chance of achieving victory in the war. The line of advance was east of "The Angle" stone wall at various distances, e.g., the Virginians pushed the Union line back.
High-water mark of the Confederacy Wikipedia
This designation was invented by government historian John B. Bachelder after the war when the monuments of the Gettysburg Battlefield were being erected. Some historians have argued that the battle was the turning point of the war and that this was the place that represented the Confederacy's last major offensive operation in the Eastern Theater.
On the third day of the battle (July 3, 1863), Confederate General Robert E. Lee ordered an attack on the Union center, located on Cemetery Ridge. This offensive maneuver called for almost 12,500 men to march over 1,000 yards of dangerously open terrain.
Preceded by a massive but mostly ineffective Confederate artillery barrage, the march across open fields toward the Union lines became known as Pickett's Charge; Maj. Gen. George E. Pickett was one of three division commanders under the command of Lt. Gen. James Longstreet, but his name has been popularly associated with the assault. Union guns and infantry on Cemetery Ridge opened fire on the advancing men, inflicting a 50% casualty rate on the Confederate ranks. One of Pickett's brigade commanders was General Lewis Addison Armistead. His men were able to breach the Union lines in just one place, a bend in the wall that has become known as "the Angle." This gap in the Union line was quickly closed with any Confederate soldiers who had breached it being quickly captured or killed, including Armistead.
Lee's Army of Northern Virginia retreated the next day, leaving Gettysburg for Virginia. Even though the war lasted almost another two years, Lee launched few offensive operations during that time, none of them near the scale of the Gettysburg Campaign.
Monuments at the high-water mark include the High Water Mark of the Rebellion Monument, the 72nd Pennsylvania Infantry Monument, and the Vermont monument with George Stannard statue.Cushing Marker
The Alonzo Cushing Marker
indicates the "spot where Lt. Alonzo H. Cushing was mortally wounded" at the "extreme point reached by the Confederates in this, their supremest effort. … Where Cushing and Armistead lie is where the tide of invasion stops. The confederate cause is buried there.
The 1887 Lewis A. Armistead Marker
marks the spot where the Confederate General placed his hand on a Union cannon before collapsing with mortal wounds. Armistead was one of 1500 Confederate Virginians that broke through the Union line at The Angle.
NY 1st Artillery
The New York 1st Independent Artillery Memorial
 commemorates the Cowan Battery
which fired on Pickett's Charge and had a cannon temporarily captured by Armistead's troops.