Question: What Byrds member served as a guest musician on Rock Salt & Nails
Context: Steve Young (July 12, 1942 – March 17, 2016) was an American country music singer, songwriter and guitarist, known for his song "Seven Bridges Road" (on "Rock Salt & Nails" & "Seven Bridges Road").  He was a pioneer of the country rock, Americana, and alternative country sounds, and also a vital force behind the "outlaw movement" that gave support to the careers of Waylon Jennings, Hank Williams, Jr. and more.  Young was also featured in the 1975 Outlaw Country documentary "Heartworn Highways".  He was the subject of the song "The All Golden" by Van Dyke Parks.  Young's first album, "Rock Salt & Nails", on A&M, was performed on and supported by Gram Parsons, Gene Clark and other musicians from the 1969 musical community in Southern California. Strataca is a salt mine museum in Hutchinson, Kansas, United States.  It was previously known as the "Kansas Underground Salt Museum".  The museum is built within one of the world’s largest deposits of rock salt and provides the opportunity to go 650 ft beneath the Earth’s surface.  It is a unique destination attraction for exploring an environs carved from salt deposits formed 275 million years ago.  The museum is located in the Hutchinson Salt Company mine which began operation in 1923 as Carey Salt Company.  There are 14 other salt mines in the United States, but none of them are accessible to tourists. Table salt or common salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in its natural form as a crystalline mineral is known as rock salt or halite.  Salt is present in vast quantities in seawater, where it is the main mineral constituent.  The open ocean has about 35 g of solids per litre, a salinity of 3.5%. Rock Salt & Nails is the debut album by Steve Young.  It is a pioneering Country rock/Outlaw country album that was recorded in 1969, with guest musicians Gram Parsons, Gene Clark and James Burton. Byrds is the twelfth and final studio album by the American rock band The Byrds and was released in March 1973 on Asylum Records ("see" 1973 in music).  It was recorded as the centerpiece of a reunion between the five original members of The Byrds: Roger McGuinn, Gene Clark, David Crosby, Chris Hillman, and Michael Clarke.  The last time that all five members had worked together as The Byrds was in 1966, prior to Gene Clark's departure from the band.  During the reunion, the current, latter-day line-up of the band continued to make live appearances until February 1973, with McGuinn being the only member common to both versions of the group. The Rock Salt & Nails are a Celtic fusion band based in the Shetland, Scotland.  The band formed in 1992. Bahadur Khel is a village and Union Council of Karak District in Khyber Pakhtunkhwa province of Pakistan.  It is located at 33°10'57N 70°57'15E with an altitude of 548 metres (1801 feet), the village is the site of an extensive rock salt quarry.  The quarry (one mile long by half a mile broad) produce high quality rock salt suitable for human consumption.  The facility is managed by the Pakistan Mineral Development Corporation. Cheshire is a county in North West England.  Rock salt was laid down in this region some 220 million years ago, during the Triassic period.  Seawater moved inland from an open sea, creating a chain of shallow salt marshes across what is today the Cheshire basin.  As the marshes evaporated, deep deposits of rock salt were formed. Harold Eugene "Gene" Clark (November 17, 1944 – May 24, 1991) was an American singer-songwriter and founding member of the folk rock band the Byrds.  He was the Byrds' principal songwriter between 1964 and early 1966, writing most of the band's best-known originals from this period, including "I'll Feel a Whole Lot Better", "She Don't Care About Time", and "Set You Free This Time".  Although he did not achieve commercial success as a solo artist, Clark was in the vanguard of popular music during much of his career, prefiguring developments in such disparate subgenres as psychedelic rock, baroque pop, newgrass, country rock, and alternative country. "Seven Bridges Road" is a song written by American musician Steve Young, recorded in 1969 for his "Rock Salt & Nails" album.  It has since been covered by many artists, the best-known version being a five-part harmony arrangement by English musician Iain Matthews recorded by the American rock band Eagles in 1980.
Answer: Gene Clark