<prompt> Translate the following text to EnglishMwanzoni mwa karne ya 19 Rafael Rivera, aliyekuwa mchunguzi wa Mexico, alivumbua bonde la mto la Las Vegas na kulipa jina la Kihispania Las Vegas na hivyo kuwafanya wageni wengi wa kisasa wajiulize ni wapi hasa malisho hayo yaliko.  <response>: It was not until 1829 that Rafael Rivera, a Mexican scout, found a spring-fed valley and dubbed it Las Vegas a Spanish name that leaves many modern visitors wondering exactly where the meadows really lay. 