(written from a Production point of view)
Griffith Park is a large park located in Los Feliz, Los Angeles, California. It was used as filming location for several Star Trek episodes. The Griffith Observatory is also located in the Griffith Park.
Star Trek locations
On 29 May 1987, director Corey Allen shot the very first day of shooting for the Star Trek: The Next Generation pilot episode "Encounter at Farpoint" at Griffith Park. The scene included actors Jonathan Frakes, Brent Spiner, and Wil Wheaton and stood in for the scenes on the holodeck. (Star Trek: Deep Space Nine Companion)
In April 1993, director David Livingston chose the location of Fern Dell, a section of Griffith Park, as location for the Monastery of the Kai in the Star Trek: Deep Space Nine episode "In the Hands of the Prophets", the last episode of the first season. The scene involved Avery Brooks and Philip Anglim and their "first meeting" in the series. According to Livingston, he was able to do a location shoot because of the high budget for the episode and he chose Fern Dell which is close to the studio. It was the easiest location for a director to shoot because of its narrow path that restricts movement which prohibits wider shots, according to unit production manager Robert della Santina. (Star Trek: Deep Space Nine Companion)
In August 1993 director Peter Lauritson filmed several scenes at Cedar Grove, a section of the Griffith Park, for the TNG Season 7 episode "Gambit, Part I". The location stood in as surface of Barradas III. Due to a fire ban on live explosives at the location, all explosions were done in post production. (Star Trek: The Next Generation Companion)
In 2004, on their second day of shooting, Monday 26 July 2004, the production team of the Star Trek: Enterprise episodes ENT: "Storm Front", "Storm Front, Part II" went on location in Griffith Park to film the wood scenes between the Enterprise crew and the Na'kuhl and Nazi soldiers.
Bronson Canyon, part of Griffith Park, has become famous as a location for several movies and television series. It was used many times for location shoots in all five live action Star Trek series as well as the movies.
In 1967, the Bronson Canyon was used as a filming location for two Star Trek episodes, "This Side of Paradise" (filmed on Friday 13 January 1967), and "Bread and Circuses" (filmed on Tuesday 12 September 1967 and Wednesday 13 September 1967).   
Also in 1991, the canyon was used as a location for The Next Generation fifth season episode "Darmok". The location stood in as the surface of El-Adrel IV in this episode. The scenes were filmed on Tuesday 23 July 1991 and Wednesday 24 July 1991 under director Rick Kolbe and with Patrick Stewart, Paul Winfield, Rex Pierson, stand-ins Dennis Tracy and James Washington, stunt double Gerard Williams and stunt coordinator Dennis Madalone. The call sheet for the first day has the note "Dress Appropriately for bees, rattlesnakes and hot sun" and is listing the sunrise at 5:58 am and the sunset at 8:01 pm. The call sheet also has an attachment, a map of the area and the way from the studio to the location.
The same year the production of The Next Generation returned for the episode "Ensign Ro" to this location just a few days after it was filmed for "Darmok". In this episode the location stood in as the surface of Valo II and its Bajoran settlement. Twenty-one background performers, Patrick Stewart, Brent Spiner, Michelle Forbes, Michael Dorn, and Scott Marlowe were directed by Les Landau and assistant director Arlene Fukai on Monday 5 August 1991 with a crew call at 6:00 am and a shooting call at 7:00 am. Sunrise at this day was at 6:07 am and sunset at 7:50 pm Birds & Animals Unlimited provided the twelve guinea fowls seen in several scenes. An almost identical map as the one used for "Darmok" was attached to the call sheets for this day. Also on location were photo doubles Ron Large and Lanier Edwards who filmed several close-ups for "Darmok".
The cast and crew of The Next Generation returned to Bronson Canyon for filming a brief scene for the fifth season episode "The Inner Light" in late-March 1992. The scene was later upgraded with a matte painting. (Star Trek: The Next Generation Companion)
In September 1993 the team of The Next Generation filmed for two days at the Bronson Canyon scenes for the seventh season episode "Attached" where it stood in for the surface of the planet Kesprytt III. (Star Trek: The Next Generation Companion)
During the location shooting in Griffith Park's Bronson Canyon for the seventh season episode "Homeward" in which the location stood in as surface of Boraal II the crew had to break the filming on 2 November 1993 because of the heavy wildfires in that area. According to line producer Merri D. Howard, director Alexander Singer was thankful that the area they've chosen did not burn down and that it was not necessary to search a similar location. (Star Trek: The Next Generation Companion)
In 1995 the production of the Star Trek: Voyager episode "The 37's" moved to Bronson Canyon to shoot several scenes there. The surface scenes of the unnamed Delta Quadrant planet and the landing and starting of the USS Voyager were filmed in the Bronson Canyon. The VOY Season 2 DVD trivia text version of "The 37's" featured several information about the location: TNG: "Darmok" and Star Trek VI: The Undiscovered Country were filmed there and the place is a famous filming location since the 1930s including productions such as The Scorpion King, The Searchers, Invasion of the Body Snatchers, Bonanza, Gunsmoke, and the well-known home for the Batcave in several Batman features.
Regarding Voyager standing beside the mountains, special effects supervisor Dan Curry said that he used a foam core mock up to plot camera angles and perspectives of the Voyager matte painting. For the scenes showing Voyager, the special effects team had to digitally remove the legendary Hollywood sign for some scenes.