Since some cities in western America like Seattle has only one supertall tower proposed or built, it's unnecessary to write a post for only one building and they can't be ignored as well, therefore they are integrated into this post. Skyscrapers in the cities west of Mississippi in America have always been much less than in those cities in the east no matter in terms of completed ones or ones that are under construction.
There are many reasons behind this, first is earthquake as these west coast cities are all located in San Andreas Fault. Although in fact earthquake can not really destroy a tower, but it still can hold some new proposals back by the fact that it could significantly raise the cost of construction and maintenance, this is also arguably the same reason for the lack of supertalls in Tokyo, which is another renowned city located in the earthquake zone, though flight path issue is another reason for it.
Secondly the shadow issue is also a great enemy of skyscrapers, this is more obvious in San Francisco, the Salesforce Tower was once planned to stand 370 m or 1200 ft tall, and reduced to 326 m due to the shadow it may produce. California is known for its sunshine, people live there are generally more favor of natural views but not tall buildings.
Thirdly the issue of flight path is also a great factor, the Columbia Center, which is currently 2nd tallest building in western America, was once planned to rise to 306 meters tall, but later got a cut on height making it finally topped out at 285 meters, only 15 meters from the supertall mark. The newly proposed 4/C Tower has also been reduced in height for the same reason.
There are more other reasons, people in California seem tend to live in cottages but not high rises, which can also leads to less skyscrapers proposals since nowadays new proposals in American cities like New York City are primarily for residential use.
In some science fiction films like Blade Runner, Los Angeles is depicted as a place crowded with megatall towers, buildings with a height of higher than US Bank Tower are commonly seen across the city and are dwarfed by other towers, however unfortunately Los Angeles has never been affected by this movie, the skyscrapers in Los Angeles are still centralized in Downtown, and no proposals for supertall that exceeding 300 m by roof height ever came out till today except the US Bank Tower, which was merely built as part of redevelopment for Central Library Area because of the fire disaster, while many other cities around the world has been undergoing a variety of construction booms.
1. Stratosphere Tower
Standard height: 350 meters,1149 foot
Roof height: 280 meters
Built year: 1996
Location: Las Vegas
Architect: Paul Steelman Design Group
Though not being regarded as a habitable building, Stratosphere Tower still belongs to supertall category with a height of 350 meters, in the same time it remains the tallest free standing structure west of Mississippi in America.
Standard height: 310 meters,1018 foot
Roof height: 310 meters
Built year: 1990
Location: Los Angeles
Developer: Maguire Properties
Architect: Pei Cobb Freed & Partners
Tallest building in California and the whole western America area with a height of 310 meters by both roof height and architectural height, its height by the latter measurement will be surpassed by another supertall being built in Los Angeles several months later.
Under Construction and Proposed:
1. Wilshire Grand Tower
Standard height: 335 meters,1099 foot
Roof height: 280 meters
Observation deck: 250 meters
Estimated top out year: 2016
Location: Los Angeles
Developer: Martin Project Management
Architect: AC Martin
The tower will take over the title of tallest building west of Mississippi from US Bank Tower upon completion.
Although it is touted to be the next tallest building west of Mississippi, both of its roof height and observation deck are all much lower than US Bank Tower.
The building has structurally topped out in July 2016.
2. Salesforce Tower
Standard height: 326 meters,1070 foot
Estimated top out year: 2017
Location: San Francisco
Developer: Boston Properties, Inc. and Hines
Architect: Pelli Clarke Pelli Architects
The tower was formerly known as Transbay Tower, which had been replaced by Salesforce Tower since Salesforce Group became the anchor tenant as it leased a large portion of floors in the building.
3. 4/C Tower
Standard height: 314 meters,1029 foot
Roof height: 314 meters
Estimated top out year: 2019
Developer: Crescent Height
Architect: LMN Architects
This tower was originally designed to be more than 400 m when first proposed, unfortunately the height was reduced drastically to 314 meters due to the concerns by the Federal Aviation Administration of a flight path nearby, same thing had also ever affected the Columbia Center's height.