Rangers posed for pictures with a thermometer showing temperatures reaching 56 degrees in Death Valley, California.
More than 1500 record-high temperatures were recorded in the US this month, according to the National Oceanic and Atmospheric Administration.
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Over 35 daily high-temperature records were broken on Sunday alone, according to the weather service.
Phoenix and Tucson, Arizona; El Paso, Corpus Christi and Brownsville, Texas; and Tampa and Fort Myers, Florida, are all having their hottest Julys on record to date, according to NOAA climate data.