The Carson-Douglas football rivalry, already the most storied showdown in Northern Nevada, picked up some more credibility with the rest of the state over the last month.In the preliminary rounds of national contest conducted by USA Today, the Senators and Tigers won the Best High School Football Rivalry in the state of Nevada by carrying a whopping 86 percent of the vote over Bishop Gorman-Palo Verde (3 percent) and Moapa Valley-Virgin Valley (11 percent).Carson and Douglas gathered 7,124 votes on the USA Today Web site, compared to 874 for Moapa Valley and Virgin Valley and 265 for Bishop Gorman and …