The nervous energy was palpable as hundreds of cyclists, clad in brightly colored Lycra, awaited the start of the 50-mile ride known as the Half-Century from the Santa Fe Railyard, a hub of art galleries, restaurants, and a weekly farmers market in Santa Fe, New Mexico. Then, finally, we were riding through town with eight motorcycle cops ahead of us, patrolling the intersections.We passed the Roundhouse, where the New Mexico Legislature meets. We passed Museum Hill, where four museums explore the Native American Southwest, the Spanish colonial past, and more. Then, finally, after a dozen miles or so, Santa Fe was far away and we were alone, riding through rolling ranchland.It was the second day of a two-day cycling event that each spring attracts more than 1,500 participants, who come for...