Died crossing the Platte River

When my out-laws (in-laws who live in Nottingham) retired, we suggested to Mum that she research her family, which she did very well, and that was before all this Internet stuff, although she embraced the new technology very quickly. When Freeserve started, they were keen to show us how it all worked, so I had a demonstration which involved searching for my ancestors. Somehow we found my great father on the LDS FamilySearch site with a pedigree going back to about 1500. I was bemused. So when I got home (on low-speed dial-up) I downloaded the GEDCOM and found my 4th great uncle Thomas MDGLEY had been born in Huddersfield but had died in Utah - that explains it I thought - he converted to a Mormon. Then I noticed the entry for his wife Ellen, nee HINCHLIFFE - "died 4th Sep 1855 crossing the Platte River Wyoming, buried 4th Sep 1855 at the side of the Platte River Wyoming". I just had to find out more...