The sire of Gunrock, Rock Sand (1900–1914), was a prominent English Thoroughbred race horse and sire of his time. In a career which lasted from the spring of 1902 until October 1904, he ran 20 times, and won 16 races. He was a leading British 2-year-old of his generation, winning the 2,000 Guineas Stakes, the Epsom Derby, and the St. Leger Stakes. He won another series of major races as a 4-year-old before being retired to stud, where he had success in both Europe and North America. Rock Sand's bloodline would also help establish the Selle Français, the national sport horse breed of France, as well as the Holsteiner, Bavarian Warmblood, and other German warmblood breeds in Germany.

The dam of Gunrock, the stakes race mare Gunfire, was sired by Hastings (1893–1917), an American Thoroughbred racehorse and stallion foaled in Versailles, Kentucky, and bred by Dr. John D. Neet. Originally bought for $2,800 at a yearling auction by David Gideon and John Daly, Hastings was sent to New York and raced for the partners successfully as a 2-year-old, winning several races before the partnership was dissolved by public auction. Hastings was then purchased by August Belmont Jr., for a record $37,000.^[8] His record at four was 12 starts, 4 wins, and 6 places, carrying weights as high as 140 pounds. He was retired to Nursery Stud outside Lexington, Kentucky, and became one of the most successful sires of 1902 and 1908. Of his offspring, the most notable are stakes race winners Gunfire, Field Mouse, Masterman, and Fair Play, sire of Man o' War.

Gunrock was 4x5 linebred to Springfield (1873–1898), a successful English Thoroughbred racehorse that won 14 consecutive races and was a useful sire of the late 19th century. He was the grandsire of two English Triple Crown winners: Galtee More, who was exported to Russia, and later Germany; and Rock Sand, who was exported to the United States, and in turn was the grandsire of Man o' War (1917–1947), widely considered one of the greatest American Thoroughbred racehorses of all time.

Gunrock was also 5x5x5 linebred to Stockwell on his sire's side, with additional blood from Stockwell on his dam's side as well, and linebred 6x6x6 to King Tom overall.

Gunrock covered 476 mares during his stud career, which lasted from 1921 to his death in 1932. While U.S. Army Remount stallions were officially not allowed to produce racing stock,^[9] he is most notable as a sire of Thoroughbred broodmares, with the racing mare Sugar Pie (1928) being his most successful recorded offspring.

Some of his descendants include, but are not limited to:

• Queen Roxie (1922), mare out of Queen Fay, by King William (Spendthrift line) (7-0-0-0 record, unplaced)
• Lake Rock (1923), mare out of Maria Mortlake, by Mortlake (Hampton line)
• Rockada (1926), mare out of Cruzada, by Cruzados (Emperor of Norfolk / Lexington line)
• California Nora (1927), mare out of Norette, by Norito (Emperor of Norfolk / Lexington line)
• Lady Rock (1928), mare out of Lady Lioness, by Wherewithal (Wenlock / Lord Clifden line)
• Sugar Pie (1928), mare out of Tooters, by Light O' My Life (Hampton line) (47-1-2-4 record, won $550)
• Juanita G (1928), mare out of Satisfaction, by Gargantua (Bend Or line)
• Gunita (1929), mare out of Norette, by Norito (Emperor of Norfolk / Lexington line)
• Little Pebbles (1931), stallion out of Cruzada, by Cruzados (Emperor of Norfolk / Lexington line)
• Roxey Payne (1932), mare out of Helen Payne, by Albert Jones (Sainfoin / Springfield line)
• Roxalyce (1932), mare out of Cruzada, by Cruzados (Emperor of Norfolk / Lexington line)
• Gunrunner (1932), mare out of an unknown dam

One of his male-line grandsons through Little Pebbles, Paco (1941), was exported to Uruguay in South America, where he sired the Thoroughbred stallion Adalid (1956), who had issue. Adalid had 51 starts, 3 wins, 9 places, and 7 shows during his racing career. His most successful descendants are the American Thoroughbred gelding Dogie (2000), who won $100,201 USD during his racing career (41-7-9-10); and the mare Ten Pinkies (1987), who had 20 starts, 5 wins, 2 places, and 2 shows ($14,500 USD in winnings), who also went on to become a successful broodmare, with six of her offspring winning a collective $410,485 USD.

Little Pebbles' most successful daughter, Honey Bravo (1944), has descendant Ozone Gal (1987), a Thoroughbred mare who, while not successful as a racer herself, produced six offspring who won a collective $100,258 USD.

Patricia Erigero, a 1971 UC Davis graduate and owner of the Thoroughbred Heritage site, also owned a champion Thoroughbred show horse named Bay Sands (1956), who descended from Gunrock through his daughter, Rockada (1926), out of the mare Cruzada (1917). Cruzada was a granddaughter of Emperor of Norfolk (1885–1907), a champion Thoroughbred racehorse called the "California Wonder".^[10]

While Gunrock primarily covered Thoroughbred mares, "half-bred horses" - better known as warmblood horses today - were considered to be ideal cavalry mounts by some in the United States Army Remount Service.^[9] As such, some of Gunrock's descendants have been used to improve various warmblood horse breeds in the United States, such as the Holsteiner and Irish Draught, as well as to produce sport horses to compete in non-racing equestrian sports.

One of Gunrock's distant relatives was the world champion show jumping Thoroughbred gelding Gem Twist (1979 – 2006), who was a descendant of Gunrock's half-brother, Malachite (Rock Sand x Miss Hanover), one of the grandfathers of the Thoroughbred racehorse Count Fleet (1940 – 1973). Gem Twist has become famous in more recent years due to being the subject of cloning, with two stallion clones of the gelding - Gemini CL (b. 2008)^[11] and Murka's Gem (b. 2011)^[12] - being used for sport horse breeding programs.^[13] A third clone, Gem Twist Alpha Z (b. 2012), was exported to Belgium to stand stud and produce Zangersheide and Belgian Warmblood sport horses and show jumpers.^[14]

• List of historical horses
• List of racehorses
• Henry of Navarre (1891–1917), another Thoroughbred used by the United States Army Remount Service
• Sir Barton (1916–1937), another Thoroughbred used by the United States Army Remount Service
• W. K. Kellogg Arabian Horse Center at California State Polytechnic University, Pomona (Cal Poly Pomona)

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