Since gold was found in the Sierra Nevada Foothills, visitors have been attracted to Nevada County for a wide variety of events and activities.

Every January the South Yuba River Citizen's League (SYRCL) hosts The Wild and Scenic Environmental Film Festival sponsored by Patagonia.  This is the largest film festival of it's nature in Northern America and attracts filmmakers, activists, and film buffs of all ages. http://www.syrcl.org 

Joe Cain Day is part of the Mardi Gras celebration held in February or early March. A lively, masquerade ball, held at the Miner's Foundry in Nevada City. A bead throwin', horn blowin'  parade in memory of Joe Cain(the man who brought Mardi Gras back to the United States because he too loved a good party) is another highlight. 

The International Teddy Bear Festival (..), the Railroad Museum, http://www.ncngrrmuseum.com, and the  North Star Mining Museum are among the museums and activities that attract hobbists and historians of all ages.

June's annual Nevada City Bicycle Classic Bike Race attracts  world class racers and enthusists ..from around the world http://www.nevadacityclassic.com.   

The Nevada County Fairground hosts a number of festivals and events throughout the year that attract returning guests
Music in the Mountains http://www.musicinthemountains.org
Bluegrass festival
World Music Festival http://www.worldfest.net
KVMR Celtic Festival http://www.kvmr.org/celticfestival  

Multiple venues for live music and theatre (including the Nevada City Theatre,Foothill Theatre, and the Center for the Arts,) art walks,great restaurants (Dorado Chocolates too!) grower's markets, living history days (Malakoff Diggins State Park), there's something for every visitor.

Need more info? 
http://www.nevadacitychamber.com
http://www.grassvalleychamber.com