The state medical examiner will determine if heat was a factor in a man's death.
Three people taking pictures of graffiti along the Arkansas river found his body under the 21st Street Bridge near Riverside.
Police say the man, in his 40s or 50s, was homeless and appeared to be living at a campsite.
They say there are no signs of foul play, no trauma to the body and no signs of drug use.
The man was found sitting up against a rocky embankment that gets full sun.
Police believe he may have been dead for at least a day.