The Mad River drains a portion of the coast range of Humboldt County in northern California. It runs into the ocean north of Arcata, site of Humboldt State University.  
The Mad was named by the Josiah Gregg expedition in 1849. Gregg and seven others left the Trinity River gold mines on November 5 in search of a supply route that could be served by sea. They encountered much difficulty, particularly in the coastal redwood forests, where the downed timber proved almost impassable to their mules. By the time they reached the coast they forgot their original goal and were primarily concerned with survival.

     Dr. Gregg, leader and scientist of the expedition, however, continued to spend time and effort, recording scientific data.  The others in the group were first indifferent to Gregg's scientific bent, but became progressively annoyed about it as their fortunes waned.  
When they encountered this river on December 20, Gregg stopped to record the latitude. The rest of the men wanted to cross the river and were angered by what they regarded as a meaningless delay. They set about borrowing canoes from the Indians to cross. Gregg insisted they wait until he completed his measurements. Only when they prepared to leave without him did Gregg gather his instruments and join them. He sat silently in the canoe, but once on the other side he launched into a tirade of criticism of his men.
       L.K. Wood, a member of the party later wrote: Several times during the ebullition of the old man's passion he indulged in such insulting language and comparisons, that some of the party, at best not too amiable in their disposition, came very nearly to inflicting upon him summary punishment by consigning him, instruments and all, to this beautiful river. This stream, in commemoration of the difficulty I have just related, we called Mad River.