What cities are around the valley bordering Lake Mead?
SELECT DISTINCT ?uri WHERE { ?x <http://dbpedia.org/ontology/border> <http://dbpedia.org/resource/Lake_Mead> . ?x <http://dbpedia.org/ontology/city> ?uri  . ?x <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/Valley>}
Lake_Mead