It’s national economic crisis-based, according to Dreyer’s (PDF).
At the time of Rocky Road’s birth in 1929, almost all ice cream was made in three flavors ““ vanilla, chocolate, and strawberry ““ and was always served as sundaes. Dreyer added walnuts (later replaced with almonds) to his chocolate ice cream and, using his wife’s sewing shears, cut marshmallows into bite-sized pieces to make the first batch of Rocky Road. Dreyer and Edy picked a flavor name to give folks something to smile about in the face of the Great Depression. Rocky Road became America’s first blockbuster flavor and remains one of the best-selling flavors of all time.
I wish there were a few more sources for the naming. As Wikipedia points out, there’s at least one alternate story about the ingredients. But Google turns up nothing more … except a book called The Strategic Use of Stories in Organizational Communication and Learning interviews a Dreyer’s ethic chief and the author notes on the Rocky Road story, “It’s not a long drawn out narrative, yet the imagery is rich and generates associations.” Various results in Google News put the invention a few weeks after the stock market crash in ’29, but none are sourced.
Building off this story/legend/whatever, Edy’s-Dreyer’s is now running a contest where you help introduce a national economic crisis-based flavor and get $100,000 to turn around your Rocky Road of a life.