Climate: A Greener Western united states

Question

In this scenario, I've done the following changes to the western United States.

1) Only the Rockies stand firm, so no Sierra Nevada or Coast Range.

2) The coastline has altered as though 75 meters of sea level have risen.

3) The ancient lakes of Bidahochi, Bonneville and Lahontan have been reviatalized.

4) The Channeled Scablands have become a sea.

Using these changes, what kind of climate would the Wild West have?

Had to update because someone wasn't being clear. I'm after the WESTERN United States, as in from the Rockies to the Pacific coast. Also, I'm aiming for CLIMATE, not HISTORY.

Answer 1

This is really a comment to Thucydides' answer, but I couldn't fit it in, or make it clear without paragraphs.

Re "Most of what you describe would mean "The Great American Desert" would not exist, so there would be no traditional tall grass prairies." That's not really the case, since that term is used to describe the area EAST of the Rockies, which would still exist in the OP's scenario. See e.g. https://en.wikipedia.org/wiki/Great_American_Desert

Since the Rockies would still provide their rain shadow effect, I THINK* that the Great Plains would be much like today, though perhaps a bit wetter. However, it's not really lack of water that made them grasslands, it was grazing by herds of tens of millions of buffalo (and their Pleistocene predecessors). Grasses and many forbs can be grazed to the ground, and will grow again from the roots (just as your lawn needs regular mowing). Few trees can do this, and those that can will remain as shrubs if subjected to regular grazing.

The area west of the Rockies would not be like the area east of the Mississippi, either. Most of the West has a Mediterranian climate: rain/snow fall in winter, while summers usually see only the occasional thunderstorm. This is driven by general atmospheric circulation & the Pacifc Ocean, so wouldn't change much. You'd still get the same total precipitation, but it'd be spread between the coast & Rockies. The general climate might be rather like southern France or Italy.

You'd also have quite a bit of rain shadow effect from the Great Basin ranges (many of which aren't all that much lower than the Sierra), and from the elevation of the continent itself. Remember that the valley floors in much of the Great Basin are mostly at 4000-6000 ft (1200-1800 m).

As for the large endorehic lakes like Lahontan & Bonneville, it's surprising that their existence wasn't because of higher rainfall, but cooler temperatures leading to lower evaporation.

WRT human settlement, note that most people didn't settle in the intermountain west/Great Plains until well after the Civil War. They passed through on their way to the gold fields of California (and later isolated mining camps elsewhere, e.g. Virginia City), or fertile farm lands in western Oregon/Washington.

*Absent a good climate model, this has to be just educated guesses :-)

Answer 2

Most of what you describe would mean "The Great American Desert" would not exist, so there would be no traditional tall grass prairies.

Settlers entering the "Great American Forest" would have much different conditions to cope with. No tall grass prairies would be a blessing in the sense that building materials would always be close at hand (just cut down some trees), and the severe climates of the continental interiors would be much moderated. On the other hand, settling the West would be much longer, since the land would have to be laboriously cleared in order to farm, and large scale free range cattle drives or ranching would be difficult. There wold be few or no cowboys in this West.

Settlers would also be able to use many of the skills from settling the coastal regions, since much of the wildlife would also be similar to the woodlands of the East coast; deer and small game rather than herds of Bison, for example. This also means the "human terrain" would also be different; the American Indian tribes of the interior would have lifestyles far more similar to the East coast tribes like the Iroquois rather than the sorts of lifestyles we associate with tribes like the Lakota Sioux. The great "Indian wars" of the late 1800's would not be long sweeping cavalry campaigns carried across thousands of miles, but rather a series of infantry battles in contested woodlands, carried out by lightly armed groups of soldiers much like "Roger's Rangers" in the pre revolutionary war period.

The Spanish and French settlement of the West and Sourthwest in the 1600's and 1700's would also be very different , and it might not be possible for the American settlers to eject them from the Great American Forest without an even greater disparity of numbers. How willing vast numbers of settlers would be to cross the Appalachians into the Great American Forest would be difficult to guess, other considerations like the outcome of the Seven Years War and dynastic wars in Europe would have to be considered.

This would also have an effect on the American Civil War, as the Army of the West and the Confederate armies of the Western Theatre would have different characteristics, being more attuned to fighting in dense brush and forests rather than open plains. As Sherman moves into the cleared and cultivated parts of the South, they can reform to recreate the "March to the Sea", but the Army of the West would be smaller and made up on far more raiding and scouting units; the entire army would be "bummers" scorching the land rather than a core formation to @ 60,000 surrounded by skirmishing "bummers")

Overall, replacing the tall grass prairies and the Great American Desert with the Great American Forest wold make the settling of the American interior a longer and more difficult process. The closing of the American Frontier might even be delayed until the early 1900's, rather than the 1870's, as people slowly cleared plots and cultivated their land in the vast continental forest.

Answer 3

Difficult to give a precise answer without seeing the map, and with no info about avg. global temps, and ocean currents, but here goes.

If you also have subtracted the Cascades, pretty much everything north of 40 N latitude would be like Western Europe north of 42 N latitude (Northern Portugal, north coast of Spain, west coast of France). Warm summers with some rain; mild-to-cool winters with much more rain. If the Cascades still exist, then the northern Great Basin would probably remain relatively arid (Koppen Bsk) but less than now. South of 40 N latitude means that a Mediterranean climate (Koppen Csa/Csb) would extend farther inland into what is now Nevada. Hot, very dry summers, mild, moist winters. The western slope of the Rockies would receive significantly more rain, with more runoff flowing west and southwest. A good analogy is the current climate of Turkey or the northern interior of Spain. The farther away from the Pacific, the less rain the land would get, producing a Koppen Bsh climate (steppe rather than true desert) from central Nevada to Utah. The Rockies would have more snow on them, and there might more Glacier Park like areas north of 40 N latitude.

The land east of the Rockies would probably have a very similar climate, but the east-flowing rivers would have great flow volumes.

Hope this helps.