(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 Friday 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 Fern Dell, Griffith Park. The scenes included actors Jonathan Frakes, Brent Spiner, and Wil Wheaton, Stunt Coordinator Erik Cord, and stunt doubles Bob Brown and William Perry. On the daily production report the exteriors were named "Ext. Parkland", the setting on the holodeck. (Star Trek: Deep Space Nine Companion (p. ?); daily production report)
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 (p. ?))
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 (2nd ed., pp. 265 & 266))
In April 1994, the outdoor scenes depicting the surface of an unnamed Gamma Quadrant planet were filmed at Griffith Park's bird sanctuary for DS9: "The Jem'Hadar", directed by Kim Friedman. (Star Trek: Deep Space Nine Companion (p. ?))
On Wednesday 21 February 2001, production on Star Trek: Voyager filmed scenes for the seventh season episodes "Natural Law" in Griffith Park. The location stood-in as the jungle surface of Ledos. (Call sheets)
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 from the 1930s, such as The Scorpion King, The Searchers, Invasion of the Body Snatchers, Bonanza, Gunsmoke. It's also well-known as the location of the Batcave in the 1966-68 Batman series. It was used many times for location shoots in the first five live action Star Trek series as well as the movies.
In 1967, 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 listed 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 guineafowl 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 augmented with a matte painting. (Star Trek: The Next Generation Companion (2nd ed., p. 204))
In September 1993 the team of The Next Generation filmed scenes for the seventh season episode "Attached" for two days at Bronson Canyon, where it stood in for the surface of the planet Kesprytt III. (Star Trek: The Next Generation Companion (2nd ed., p. 272))
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 chose did not burn down and that it was not necessary to search a similar location. (Star Trek: The Next Generation Companion (2nd ed., p. 279))
In December 1993, the Star Trek: Deep Space Nine episode "Shadowplay" utilized Bronson Canyon as the location for the outdoor scenes at the Yaderan settlement. (Star Trek: Deep Space Nine Companion (p. ?))
Later the same year, 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 Bronson Canyon. The VOY Season 2 DVD trivia text version of "The 37's" featured several pieces of information about the location. 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 from some scenes.
In July 2001, the Bronson caves were used as the location for the Archer IV cavern interiors in the Star Trek: Enterprise episode "Strange New World". (Star Trek Encyclopedia (4th ed., vol. 1, p. 38))