Q. According to the Sefer Hayomam’s shita, is there “nigrar” (pulling or shlepping land areas) to include Alaska west, to the rest of the American continent or do the people in west Alaska have to keep two days Shabbos?

A. See prior answer in regards to the three main opinions on the Halacha dateline. The first mentioned was the Chazon Ish zt”l view who maintains that the Dateline is six hours (90) degrees) east of Jerusalem. This coincides with the eastern edge of the major land mass Israel is located on. In addition, he posited from reason that the Halacha Dateline must take into account the unity of the contiguous land mass Eretz Yisroel is a part of. The Halacha Date Line is at the K’tze Hamizrach, but it cannot cut through land because then one person will be observing Shabbos while his neighbor is observing another day.  Therefore, he maintains that the Halachic Dateline is at the end of the continent on the border between the coast and the Pacific Ocean so that it does not cut through any land Thus, it is not only the 90 degrees that is critical but also the end of the landmass traversed by the Halacha Dateline would have the same day as their western, or Israel, side. This principle is called “graira”
Therefore, according to the Chazon Ish, Northeastern China, Korea, eastern Siberia and Australia would be included notwithstanding that the Halacha Dateline passes through them or west of them; they are part of that land mass and thus incorporated by graira into the Israel time frame.
Poskim disagree if the Sefer Hayomam agrees to the graira principle. If graira is applied then all of the mainland of Alaska is in the same day zone as the rest of America (See Noam 14: p. 79). However, according to the opinion that graira only applies to the landmass contiguous to Eretz Yisroel or to the east of it, the Dateline would run very close to the city of Central, AK (144º41’44’W) and, therefore, most of Alaska, including Anchorage and Fairbanks, would be on the western side of the Dateline.  Either way, Juneau is on the eastern side and the same day of the week as the rest of the continent. For a full discussion, see Sefer Taarich Yisroel 1:15.
In addition to the above opinions, Rav Isser Zalman Meltzer, Rav Zvi Pesach Frank zt”l ( Har Zvi 1:138) and Kav Hata’arich HaIsraeli opine that we should follow the long established day of the week, that the country of abode and the Jewish inhabitants therein, are already keeping. 
Horav Shlomo Miller’s Shlit”a opinion is that the established communities in all of Alaska should maintain the Shabbos day as they are accustomed to observe, following also the opinion of the Chazon Ish.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a