Narcissa Whitman, one of four missionaries on their way to historic and tragic roles in history, wrote this about the crossing in August of 1836: "We have come fifteen miles and have had the worst route in all the journey for the cart. We might have had a better one but for being misled by some of the company who started out before the leaders.
“It was two o'clock before we came into camp. They were preparing to cross Snake River. The river is divided by two islands into three branches, and is fordable. The packs are placed upon the tops of the highest horses and in this way we crossed without wetting. Two of the tallest horses were selected to carry Mrs. Spalding and myself over. Mr. McLeod gave me his and rode mine. The last branch we rode as much as half a mile in crossing and against the current too, which made it hard for the horses, the water being up to their sides. Husband had considerable difficulty crossing the cart. Both cart and mules were turned upside down in the river and entangled in the harness. The mules would have been drowned but for a desperate struggle to get them ashore. Then after putting two of the strongest horses before the cart, and two men swimming behind to steady it, they succeeded in getting it across.
“I once thought that crossing streams would be the most dreaded part of the journey. I can now cross the most difficult stream without the least fear. There is one manner of crossing which husband has tried but I have not, neither do I wish to. Take an elk skin and stretch it over you, spreading yourself out as much as possible, then let the Indian women carefully put you on the water and with a cord in the mouth they will swim and draw you over. Edward, how do you think you would like to travel in this way?"
John C. Fremont told of another crossing in 1842: “About two o’clock we had arrived at the ford where the road crosses to the right bank of the Snake River. An Indian was hired to conduct us through the ford, which proved impracticable for us, the water sweeping away the howitzer and nearly drowning the mules, which we were able to extricate by cutting them out of the harness. The river is expanded into a little bay, in which there are two islands, across which is the road of the ford; and the emigrants had passed by placing two of their heavy wagons abreast of each other, so as to oppose a considerable mass against the body of water.”
Fremont mentions just two islands, not three. Like other travelers he probably ignored the third island, using just two to make his crossing. The interpretive center at Three Island Crossing State Park tells the story.
One thing not related to the famous crossing at all frustrates rangers there. In recent decades the name Three Island Crossing is often confused with Three Mile Island in the minds of those who remember the nuclear accident that happened a continent away.