According to the Erie RR operating timetable, the Orange Branch began at Forest Hill on the Erie’s Newark Branch. To elaborate a bit on the Newark Branch, AFAIK there is still freight service on the western (geographically northern) section. Its drawbridge across the Passaic is just upstream from the M&E bridge and I-280 in Newark, but has been in the open position for decades, so this section is not in service. All the Erie lines, including the original “main line” through the city of Passaic, the “Bergen County RR”, and the branches such as the Northern Branch, New Jersey and New York RR (Pascack), Orange, Caldwell, Newark, and Greenwood Lake lines, all ran to the Erie’s terminal in Jersey City — gone since about 1958 when the Erie’s trains moved to the Lackawanna’s Hoboken terminal, anticipating the merger of the two railroads into Erie-Lackawanna. (The NY Susquehanna & Western also used the Erie’s terminal, but its trains never moved due to lack of a direct track connection; the Northern Branch, to Nyack, also suffered from a direct connection and required a backup move to get to Hoboken.) The Jersey City terminal is at the location of the current PATH Pavonia-Newport station, originally called “Erie,” and unless something’s happened the letter E still stands on the original columns on the platforms.
The former Erie and Lackawanna lines have been much realigned over the years. The Lackawanna’s Boonton Line, IIRC conceived as a freight bypass of the congested commuter main line Dover-Hoboken but also used by some passenger trains, was abandoned through Paterson and replaced by the current Interstate 80. South (railroad east) of Paterson through Hoboken the line very much still exists, and is called NJT’s “Main Line,” an echo of the Erie’s original Main Line through Passaic — which was abandoned and its trains rerouted onto the former Lackawanna Booonton Line to eliminate the troublesome grade crossings through the city of Passaic. Even though the line today may seem to be for ex-Erie trains (to places like Suffern and beyond), stations such as Delawanna should let you know of the Lackawanna heritage. To connect the “real” Erie Main Line in the city of Paterson to the “new” ex-Boonton line, trains operate over a short stretch of what was the northern (RR western) end of the Erie Newark Branch. All this ahppened around 1960, I believe.
The Greenwood Lake line of the Erie started off the Erie’s main line in the Jersey Meadows. Its abandoned drawbridge over the Hackensack is immediately upstream from Portal Bridge on the NEC; the line is scheduled to become a rail-trail (if anyone can figure out how to get the users across the Hackensack!); the line then went under the NEC, clearly visible from any train today. As you wrote, it then crossed the Passaic and went through North Newark, then coming close to the Lackawanna’s stub-ended, electrified Montclair branch at that line’s terminal in Montclair. It then when north, eventually crossing the Lackawanna’s Boonton line at grade in the area of Mountain View. It continued all the way to, you guessed it, Greenwood Lake.
When the Lackawanna’s Boonton Line had to be abandoned through Paterson, its trains were rerouted on a more circuitous route, using the Erie’s Greenwood Lake line between Mountain View and Hoboken. Still later, NJ Transit finally accomplished its long-time goal of connecting the Lackawanna’s Montclair Branch to the Erie’s Greenwood Lake line at Bay Street, Montclair, which involved abandoning the original terminal, building a new station and the connection, and extending the overhead wires to Montclair State on the Greenwood Lake line; at this time service ended on the Greenwood Lake east of Montclair, although there may be some local freight service (as there is on the former Boonton Line for a few miles east of Mountain View). NJT calls this combination of Lackawanna Montclair Line, Erie Greenwood Lake line, and Lackawanna Boonton line the “Montclair-Boonton Line,” which is where we are today.
One final detail: for years after the move of Erie trains to Hoboken, the “Main Line” and “Bergen Line” (together with the Pascack Line) trains joined at a point in the Meadows; this was the site of a headon collision of an inbound Bergen Line push-pull, cab car leading, with an outbound Main Line train, diesel-hauled. The inbound engineer had successfully concealed a color-blindness problem and he ran a stop signal, colliding nearly head-on with the outbound train where their paths crossed in the junction, killing both engineers and one passenger, seated just behind the inbound train’s cab. This junction was abandoned when it became necessary to reroute the Bergen/Pascack trains over to the “Main Line” so that all could stop at the new Secaucus Junction station. And as a final reminder, although the lower level at Secaucus serves trains from the old Erie lines, it is actually located on the right of way of the original Lackawanna Boonton Line. Amtrak’s interlockings on each side of Secaucus’s upper level on the NEC memorialize the history: they are ERIE (on the east of the station) and LACK (on the west).