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. 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 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.
There are two monuments to the 150th Infantry. This one is a smaller one and chock full of relief work. The monument is surrounded by all sorts of statues, monuments and memorials along this road which overlooks a battlefield. The 150th Pennsylvania Infantry is located 366 feet off of the Lincoln Highway. If traveling southeast along Rt 30 (Lincoln Highway), make a left onto Stone-Meredith Avenue. While traveling south, the monument will be on the left or east side of the road. 
To the left is the McPherson's Barn, a one-time field hospital. Parking is available on the side of the road at intermittent cutouts or on the shoulder, which ever is available. Make sure to leave enough room for other to pass and never park on the grass or anything green or you will be ticketed by the park police.
The Smithsonian page (cited below) describes the monument a rectangular marker with an apexed cap stands on a two-tiered, rough-hewn base. There is a relief of Infantry arms and accouterments on the front face and on the top. There are two recessed disks, the insignia of the 1st Corps, flanking the inscription on the front. Below this inscription is a square tablet relief of the Pennsylvania Coat of Arms.
The sculpture and relief work is made of granite with some bronze relief work as well. Overall the statue is approximately 12 ft. x 8 ft. 4 in. x 5 ft. 5 in. I could not find any information about the artist except for who fabricated the piece which was Ryegate Granite Company. The monument was dedicated on Sept. 11, 1889.
The monument is one of 110 honoring Pennsylvania troops who participated in the Gettysburg campaign and indicates the most advanced line held by the 150th Pennsylvania Infantry on the afternoon of July 1, 1863.
There are inscriptions on all four sides which read:
(Front):150th. Penna. Infantry.
(2d. Regt. Bucktail Brigade.)
2d. Brig. 3d. Div. 1st. Corps.
(Left Side):
July 1 the Regiment held this position from 11:30 a.m. to 3:30 p.m. Present at Gettysburg 397. Killed and mortally wounded 53. Wounded 134. Captured or missing 77.
(Right Side):
Recruited in Philadelphia, Crawford, McKean, and Union Counties. Mustered in Aug. - Sept. 1862. Mustered out June 23, 1865.
(Back):This monument marks the most
advanced line facing west, occupied
by the regiment. Repeated changes
of front were made to meet
assaults from the north and west
and the right wing charged to
R.R. cut. In retiring it made
several stands and engaged the
enemy. Evening of the 2d moved
to support the left and held
position on Emmitsburg Road.
Morning of the 2d moved to
left centre and remained until
the close of battle.
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 classified as structure number MN032-B
From the Nomination Form:
1 of 75 Civil War US Brigade Tablet in Park. Records movement & itinerary of Stone's Brigade during Battle of Gettysburg, July 1-3 1863.
Short Physical Description:
Bronze inscription tablet, 4”0’ x 3’8”, attached to slant face of polished sea green granite monolith. 3’0” squared base of monument tapers to a smaller dimension at the tablet. All 5’4” H.
Long Physical Description:
Located on E side of Stone Avenue just S of Chambersburg Pike.
My Sources
1. NRHP Nomination Form
2. SIRIS
3. Stone Sentinels
4. Virtual Gettysburg" target="_blank">Virtual Gettysburg
5. Draw the Sword
6. Historical Marker Database