The 150th Pennsylvania Infantry served as a member of Stone’s Brigade in Doubleday’s Division of the First Corps, Army of the Potomac, a Fighting 300 Regiment. The first major battle that the 150th was in was Gettysburg, where it held back overwhelming numbers of confederates for several hours. On the first day of the battle, the 150th took 288 casualties out of the 397 officers and enlisted men present on McPherson’s Ridge. During the Battle of Gettysburg, the unit was commanded by Colonel Langhorne Wister (1834-1891). At Gettysburg, his unit had 397 men engaged in battle an among them 35 were killed, 152 were wounded and another 77 went missing.
Wister was in the iron business in Duncannon. During the Civil War, he first served as a Captain in the 13th Pennsylvania Reserves, then as Colonel and commander of the 150th Pennsylvania Volunteer Infantry. He assumed command of his regiment's brigade on the first day of the Battle of Gettysburg (July 1, 1863), when the fierce fighting around the McPherson House struck down previous commander Col. Edmund Dana.
The 
150th Pennsylvania Infantry Monument is located on the right or east side of Hancock Avenue (RD310) if traveling north along the road at an area called The Angle. This monument is across the road from the Battery B, 1st New York Artillery Monument (MN240-D). The monuments in this area represent the line of union regiments who defended Cemetery Ridge at The Angle against Longstreet's assault also referred to as Pickett's Charge on July 3, 1863, the final day of the Great Battle. 
Parking is plentiful and is available road-side at intermittently enlarged shoulder cut-outs, usually marked with white striping. Be sure to keep vehicles off the grass or you will be ticketed by park police. I visited this monument on Tuesday, August 7, 2012 at approximately 3:49 P.M. I was at an elevation of 583 feet, ASL. I used a Canon PowerShot 14.1 Megapixel, SX210 IS digital camera for the photos.
There are two monuments to this infantry at Gettysburg. The Draw the Sword site helped out by the NPS narrative and the SIRIS site offers the following description for this monument: Sculpture: granite; Base: granite. Denotes the 150th Pennsylvania’s position on July 3. It was dedicated in 1888. It was moved from First Day’s Field when the larger regimental monument was erected in 1889. It indicates the position held by the regiment on July 3, 1863. Monument is a two-part stepped granite shaft topped with the Corps insignia finial and set on a three foot square base. The lower part of the shaft has an excised inscription on the face and the upper part has an incised inscription of all sides. Overall height is 5.6 feet.
The monument was dedicated July 3, 1888 by the Commonwealth of Pennsylvania. The monument is composed of granite and has the following dimensions: The sculpture is approximately 5 feet 6 inches x 2 feet 4 inches x 2 feet 4 inches and the base is 3 feet 1 inch in². I was unable to find any information on the artisans who worked on this monument. There are inscriptions on all sides of the monument which read:
(Front):2d. Brigade,
3d. Div.
1st Corps.
July 2d. & 3d.
1863.
Erected by survivors
1888
2d. Regt.
Bucktail Brigade
150th. Regt. P.V.
(Left):July 1st. This
regiment fought
near Chambersburg
Pike beyond the
town, where its
monument stands,
losing 53 killed,
134 wounded and
77 missing. A total
of 264 out of
397 engaged.
(Back):July 2d. In evening
skirmished to
Emmitsburg Road
in front of this
position recovering
two guns. Remained
on skirmish line
until morning.
(Right):July 3d. Held this
position under
heavy fire until
close of battle.
Recruited in
Phila., Crawford,
McKean, & Union
Counties. Mustered
in Sept. 4, 1862.
Mustered out
June 23, 1865.
The 150th Pennsylvania Infantry Monument 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 MN247.
From the Nomination Form:
1 of 110 Pennsylvania Mn. Indicates position of 150th PA Infty July 3, 1863. Located E side Hancock Av. S of Copse of Trees near US Regulars Mn. Moved from Reynolds Av in 1889
Short Physical Description:
Mn base 3' sq. 2 part stepped granite shaft: 1st w/excised inscription on face; 2nd w/incised inscription on 4 sides. Topped w/Corps insignia finial. All 5'6"H.
Long Physical Description:
Monument is a two-part stepped granite shaft topped with the Corps insignia finial and set on a three foot square base. The lower part of the shaft has an excised inscription on the face and the upper part has an incised inscription of all sides. Overall height is 5.6 feet. Located on the east side of Hancock Avenue south of the Copse of Trees. Moved from Reynolds Avenue in 1889.
My Sources
1.
NRHP Nomination Form
2.
SIRIS
3.
Stone Sentinels
4.
Virtual Gettysburg
5.
Draw the Sword
6.
Historical Marker Database
7.
Wikipedia