The short answer is no, as has been said.
There are a few bus lines popping up.
You can check them out at http://gotobus.com and http://cashuttlebus.com .
They typically take you between SF/LA and LA/LV and that's about it.
travel.stackexchange.com/users/91/mteng
Sorry, but no.
There are parts of the western states you can get to and from via train, but they're a small percentage of the whole area.
If your goal was to, for instance, just get around the SF Bay Area, then the combination of BART, Muni, CalTrain , etc. would be sufficient.
But given that "the Western US" is about half the country (depending on where you draw the line), you're not going to find any one thing that applies to all of it.
travel.stackexchange.com/users/74/Dori
Megabus does serve California and Nevada now (since 2012).
It looks like they have service along
the I-5 (San Francisco to Los Angeles), I-80 (San Francisco - Sacramento - Reno - Sparks) and I-15
(Los Angeles to Las Vegas) corridors.
travel.stackexchange.com/users/1362/Nate Eldredge
When I traveled the east coast USA, the Chinatown bus was the budget way to travel.
It was (apparently) cheaper than Greyhound, at the cost of a little luxury (although after taking a Greyhound bus I'm not sure there were many luxuries to lose).
The Chinatown buses run from Chinatown in one city to Chinatown in another.
These were mainly an East coast thing, but they are spreading more and more to the West coast.
I've never actually been on one myself
(I got suckered into riding a greyhound), so I can't speak to their comfort and such.
these might be of use: http://en.wikipedia.org/wiki/Chinatown_bus_lines - wiki article http://www.chinatown-bus.org/ - Chinatown bus page
travel.stackexchange.com/users/121/zeocrash
I had to travel to Barstow, California on the Greyhound route between Los Angeles and Las Vegas a few times last winter
and I noticed a few other bus lines running that route.
It may be an anomaly, but it couln't hurt to research this and see of those bus lines have other routes.
travel.stackexchange.com/users/64/Keyslinger
There are many scheduled intercity bus companies in the Western US.
They include: ACN ADN Amtrak Thruway bus BoltBus Cabin CoachRun EPLA Limo FlixBus Fronteras
del Norte Hoang Express Intercalifornias Lux Bus America Los Paisanos Megabus Mexicoach TAP Royal
Tufesa Quick Shuttle On Busbud you can search and compare many of these and read user reviews to get a better idea of the quality of service.
(Full disclosure: I work there.)
travel.stackexchange.com/users/20576/Carl
A few years ago, I used to ride Greyhound for short trips, but I remember them being crammed and sometimes smelly. In the Midwest, I've learned of and used Megabus, which has seats like an airplane, outlets to plug things in, lights, air, and much more space. The best part: if I buy them early enough, I can get a several-hour trip for $10! Sadly, Megabus is not on the west coast. Is there anything at par with it over there?
Are there any good, cheap bus companies to use for traveling around the western United States?
travel.stackexchange.com
<usa><budget><buses>
travel.stackexchange.com/questions/246
travel.stackexchange.com/users/57/Eri
Companies that could offer intercity services in the Western US include ACN, ADN, Amtrak, Thruway bus,  BoltBus, Cabin, CoachRun, EPLA Limo, FlixBus, Megabus and Fronteras. Even though Megabus started work in the states of California and Nevada in 2012, this is not widespread information. However, There are many interciy bus companies like  FlixBus, CoachRun,CAN, CAN Amtrak Thruwau bus, BoltBus and Cabin that work within Western U.S
There is no equivalent to Megabus in Western U.S.  Megabus started  travelling to  the states of California and Nevada in 2012 Intercity bus companies like FlixBus, CoachRun,CAN, CAN Amtrak Thruwau bus, BoltBus and Cabin work within Western U.S