Salt and other minerals are dissolved into the water from the rocks and sand and dirt and whatnot that it travels through after it rains down, collects into streams, then rivers, and into lakes. Most lakes drain eventually into the sea, so the mineral content of this water is carried with it down to the ocean, and doesn't build up continually in these lakes.
Lakes that don't drain, however, build up minerals continually. It doesn't sound like a lot, after all, if you drank some river water flowing into one of these lakes, it wouldn't taste salty. However, if it flows in day after day, month after month, year after year, for millenia, it does in fact build up a hell of a lot of minerals.
Nightlion, have you not heard of
salinization of land due to irrigation (plus other, non-manmade processes)? If land can build up levels of salt just due to irrigation of crops over a few decades, imagine how much salt and other minerals can build up in a lake like the Great Salt Lake, or the Dead Sea, after tens of thousands, or hundreds of thousands of years by entire rivers' worth of water flowing into them and evaporating, leaving behind their salt?
Anyhow, the idea that Lake Bonneville proves Noah's Flood is a complete non sequitur. Even if salinization due to evaporation of Lake Bonneville and the contribution of salts over millenia by its tributaries aren't enough to explain the salt content, that wouldn't mean the Flood of Noah must be true. There are infinitely many other possibilities that could do such a thing, such as what the Dude mentioned, about it having previously been connected to salt water directly (though I haven't read that one before, anyone have sources?).
Finding what one thinks to be a weakness in the conventional, scientific explanation for something, and then yelling out "therefor God must have done it!" has always been embarassingly naïve, and yet it is a technique able to convince the ignorant or the unintelligent. If not, Kent Hovind and Ken Ham would be out of a job, that's for sure - but even our friend Nightlion here seems to embrace it. Nightlion, you would do well to rethink.
Mormonism ceased being a compelling topic for me when I finally came to terms with its transformation from a personality cult into a combination of a real estate company, a SuperPac, and Westboro Baptist Church. - Kishkumen