Union Pacific could have had an easier transcon grade north of Cheyenne

The CNW was building west on such a route; pert of it I think became the line known as the "Cowboy".  the CNW was trying to bypass UP to get to SP directly.

No, the C&NW was trying to get to the coal fields of western Nebraska, Wyoming, and Montana.

C&NW wound up in Lander WY, at the base of some rugged mountains.  NOT a good route choice to continue westward.

The UP would have had a lower summit if they had chosen to cross South Pass at 7412' elevation (Sherman Hill is 8013' in elevation).  This was the historic route of both the Oregon Trail and the Mormon trail.  The two trails split just west of the South Pass summit.

ChipR

A largely ignored geologic formation, the Black Hills would be in the way North of Cheyenne.  Also, there is a mainline (now BNSF) that runs across northern Nebraska and southern South Dakota that is in the way.  That line then turned north and went along the backside of the hills.

Going on the North side of the hills may of been possible, but then the UP would have had to navigate a largely empty terrain with few constant rivers (water source) or places to stop.

The next entrance north of the Hills that the UP could have used would have been on the border between North and South Dakota.

And finally, if the UP went Northwest across Wyoming then back south, that is a ton of extra miles of track, which isn't cheap to build, and Wyoming is pretty desolate in the Gillette Basin

Since the UP was one of the first railroads in the area, they 'could' have built the line differently, but with the time constraints, being maxed out on man power, and the extra cost, I don't think it would have been wise to go Northwest. 

So the answer is yes, but it it would not have been easier to build, maintain, or operate. 

The UP and CP was in a race to get as much track build as quickly as possible

After an extended search, I found a reference to and discussion of the story I saw briefly some years ago:

http://cs.trains.com/trn/f/111/t/37145.aspx?sort=ASC&pi332=1

"Union Pacific's Historical Blunder"

In 1909 the Union Pacific surveyed a cut-off from Yoder (near Joyce) to Medicine Bow along the Laramie River. This would have crossed the current BNSF (C&S) route at Wheatland, Wyoming's first permanent trading post (1834). The cut-off was not built because of the crippling effect it would have had on Cheyenne and Laramie.

Why didn't they go that route in the first place, did the surveyers miss it? Not saving 40 miles in distance and 1000 feet in altitude is a blunder in my books...

There was a better crossing of the continental divide north of the original route that was undetected. From what I’ve read, even though they didn’t get the best route the UP was very satisfied. By the standards of the day you could hardly hold the surveyors remiss. In fact, Ambrose considered their accomplishment almost heroic, considering that they were being constantly hassled by the Indians. By the time the UP found out about the better route, the whole infrastructure (including Cheyenne, WY) was too well established...

The route I am talking about is not the lousy South Pass route ... the 1909 proposed line ... would have still served all of the mines and the towns of Medicine Bow, Hanna, Rawlins, Rock Springs and Green River and still crossed the Continental Divide at Creston, 7,107'. The highest point on the Transcontinental line would have then been at Aspen tunnel to your west.

Hoping someone with a better knowledge of Wyoming geography can tell us if a railroad could have built along the Laramie River, between Fort Laramie and Medicine Bow, to avoid 1000 feet of additional climb (? see previous posts) over the Laramie Mountains?

At .83%, doesn't Union Pacific have the most favorable route crossing the Rocky Mountains? If not optimum, pretty good relative to other railroads. Recall, Rio Grande and Santa Fe encounter 3% grades on Tennessee Pass and Raton, Northern Pacific - 2% on Bozeman, Milwaukee - 2% on various grades in the Rockies and Bitterroots, and Great Northern - 1% on Marias (next most favorable). The Rocky Mountains are just a formidable barrier!

suggest you do a little more research on this subject. suggest you look into WHO was paying the "freight" or who was paying for each mile of track built. Perhaps you will find that A LOT of "unnecessary track" was built in Utah

Canadian National has just 0.4% westbound and 0.5% eastbound across the Rockies, but that's a long ways north.

Great Northern is only 1% westbound over Marias Pass, but GN's Stevens Pass has lots of 2.2%.

Union Pacific's #3 track from Cheyenne to Sherman summit (Harriman cutoff completed about 1952) is only 0.83% but about 9 miles longer, so expedited trains with sufficient power use the shorter steeper original grade.

This is an interesting document with grade charts for the more northerly transcontinental railroad ruling grades:

http://www.lexingtongroup.org/...Grade%20Profiles.pdf

Ace - Note, I specified the Rockies. The Cascades posed the next barrier, so much so, that Milwaukee and Great Northern electrified. But what a load of interesting railroading! Up in Canada, it clearly was more advantageous to be the second transcon, when it came to route selection! 

I live near the black Hills in South Dakota, so I know a little bit about east/central Wyoming.  Past medicine bow, I believe there is a pair of reservoirs, both held up by a dam.  So that tells me that the terrain is too steep.

The terrain of Wyoming is flat for the East third of the state, and then three major ranges of hills/mountains take up the rest of the state, Kind of like Colorado, but a little more flat.

The only way around that I know of would be to cross around the East side of the Laramies entering Wyoming near lusk, maybe a little north, and head west to Casper, which by the way is what the line BNSF now own does.  A quick Google search of the area and set to Google earth reveals that there are not very many paths.  Also, look where the roads are built.  They for the most part follow the rail line and will almost never climb a grade on a major highway steeper than 10%.  If there is no road built, there is little possibility for a train to make it up.

Finally, as stated earlier, water is scarce here, so steam trains would have a tough time crossing the great distances.

You can think of it like crossing a vast desert.  The original route is one of the better ones to take.

Now, I remeber something north of of the UP mainline along the western contirntial divide.  Shomewhere in WY, it splits off in two directions, then join.  In other words, water in this "divide ring" do not go to the Gulf of Mexico or Pacific.  I just sits in a bowl.  Am I correct.

Yes, the Continental Divide splits in Wyoming and forms a basin approximately between Green River and Rawlins, shown by the green lines on this map:

But this terrain is "relatively" flat and Union Pacific goes right across it. The railroads are shown as faint dottted lines on this map, highways in red.

After studying detailed topo maps, I see that the Laramie River could have provided a river-valley rail route (in yellow on this map) from the North Platte valley and through the Laramie Mountains, saving over 1000 feet of climb to go over Sherman Summit. This is approximately 70 miles north of Cheyenne and it could have been a fairly direct through route west from the Platte and North Platte Valleys.

It would be interesting to see the geography of the area firsthand, to eyeball whether it might have been feasible to build a railroad along this part of the Laramie River. There appear to be some secondary roads through that area. 

Of course, political and economic factors strongly influenced the location of the first transcontinental railroad, in particular the desire to route closer to Denver. But it required 1000+ feet of additional climb to go over Sherman Summit.