Gold Rush originated at the Purdue Horticulture Research Farm in West Lafayette, Indiana, where it was named "GoldRush" in honor of (1) its color, (2) a purported "rush" of flavor, and (3) some goofy marketing theory that says if you jam two words together and capitalize letters in the middle, more people will buy the apple.
Sorry guys, but nobody calls it that, and it is a tribute to the actual qualities of this variety, not your marketing acumen, that people like it enough to reinterpret the name back into English.
Gold Rush is a medium-sized ribbed apple with waxy yellow skin--tinged with green--flecked with dark lenticels. A light bronze blush shows where the sun has been.
The flesh is yellow, firm, and crisp, still on the coarse side but more fine-grained than that of many yellow apples. Its flavor has the honeyed sweetness of a Golden Delicious, wedded to a pleasing tartness with a touch of acidity. The tension between these flavors is just right and there are fleeting hints of pear, citrus, and spice to keep things interesting. Plus a little metalic fizz on the tip of the tongue.
This apple was really fun to eat and worth seeking out. It is reputed to be a good keeper, too.
More than you ever thought there was to know about this apple is set forth in a 1994 paper published in Horticultural Science (HortScience 29(7):827-828) and available online. The authors provide a family tree for Gold Rush that goes back six generations and includes such apple luminaries as Winesap, Melrose, and of course Golden Delicious.
There's also a soberly quantitative comparison of Gold Rush versus Golden Delicious along such dimensions as firmness, "Titratable acidity," and pH.
Update: This is not a good keeper. It is a fabulous keeper.