I hope the question makes sense. I was just looking at a map of the US and noticed that the West Coast states seemed so much larger than East Coast states and it got me wondering.

There may be several factors on a case by case basis, but one seems very important to your question. (Though I will gladly defer to someone with a specialty to this era if they chime in)

States formed after the invention of the railroad would have been much easier to govern across wipe open spaces. California and Texas are unusually large a populous because they were both independent nations when they entered the union.

Interestingly, Texas had the option of splitting up into up to 5 new states, which would have been theoretically easier to govern, though by 1850 the railroad system of the U.S. was already connecting cities as far away as Boston and St. Louis making the challenge of governing large states, and by default our large nation much less challenging.

One reason that the first states are so small is the original settlement of our nation. The original 13 states strongly mimic the original colonies. Given that this was found to be easier to govern for the time. Also, the Spanish colonies were to the south (TX, CA, NM and after the Treaty of Paris, LA, AR, OK, MO, KS, NE, IA, MN, ND, SD, WY, MO, CO, and ID), the Dutch colonies to the northeast (in CT, RI, MA, NH) and the French colonies (after 1800, LA, AR, OK, MO, KS, NE, IA, MN, ND, SD, WY, MO, CO, and ID). In 1803, the Louisiana Purchase took place and America bought this land from Napoleon. However, the purchase failed to define boundaries of individual territories.

There were several reasons why western states are larger than eastern states. One is that in the northeast, there are many more geographical boundaries (rivers, mountains). As irashandle mentioned, since there were very few settlers migrating west, mapping smaller territories would mean more government bodies. There, quite frankly, was not enough manpower to satisfy these demands. Another factor was water access. Since there are fewer water sources in the west, many states shared access to the same rivers and lakes. But also as irashandle mentions, when railroads were established, some state lines were redefined because of this.

In many of the western states, we still see geographical significance in their formation. Henry Gannett is known to be a geographical pioneer and in many of his papers, he describes the importance of each state's formation. I think the one that best describes the formation of each individual territory is Boundaries of the United States and of the Several States and Territories. In this, we see that geographical markers still played a large role in the formation of all states, including the western states.

Economic sources also played a role. Utah was originally the state of Deseret (a Mormon territory) but when silver was discovered to the west, it was cut in half to form Nevada and when gold was discovered to the east, it was cut even further to form Colorado. California drew its own line, cutting into Nevada to keep all the gold that they could from the Sierra Nevada mountain range. Another instance is the Idaho Territory which was once much larger than it is now. Montana took a large plot of land west of the Continental Divide to acquire more goldmines.

The Carolina Territory was also once much larger. Originally, it stretched across the country from coast to coast. It is largely assumed that the territory was split in 1710, the territory was split in two with North Carolina being governed by Edward Hyde. However, further research shows that Hyde likely came into office in 1711 as he was in Virginia in 1710 and pops up in North Carolina in 1711. So I would say it occurred in 1711 or 1712. Many also argue that the split resulted from the Yamasee War of the early 1700's however, this war most likely began in 1715. The last theory (the one I lean towards) is that since the two major ports [Charles Town(Charleston) and Albermarle Sound) were roughly 300 miles apart, the cultures were vastly different (the south was mostly wealthy English inhabitants and the north was mostly populated by Quakers along with harsh tobacco farmers) and the official split probably resulted because of this difference.

I am more versed in early settlement (colonial), but this is what I have learned through personal research. Each territory/state has its own unique story and I'm sure there will be others who will have far more knowledge than I on the subject. In any case, I hope this helps.