Baikal Sea Map
In 1643, Vasily Poyarkov crossed the Stanovoy Range and reached the upper Zeya River in the country of the Daurs, who were paying tribute to the Manchu Chinese. After wintering, in 1644 Poyarkov pushed down the Zeya and became the first Russian to reach the Amur River. He sailed down the Amur and finally discovered the mouth of that great river from land. Since his Cossacks provoked the enmity of the locals behind, Poyarkov chose a different way back. They built boats and in 1645 sailed along the Sea of Okhotsk coast to the Ulya River and spent the next winter in the huts that had been built by Ivan Moskvitin six years earlier. In 1646 they returned to Yakutsk.
In 1644 Mikhail Stadukhin discovered the Kolyma River and founded Srednekolymsk. A merchant named Fedot Alekseyev Popov organized a further expedition eastward, and Semyon Dezhnyov became a captain of one of the kochi. In 1648 they sailed from Srednekolymsk down to the Arctic and after some time they rounded Cape Dezhnyov, thus becoming the first explorers to pass through the Bering Strait and to discover Chukotka and the Bering Sea. All their kochi and most of their men (including Popov himself) were lost in storms and clashes with the natives. A small group led by Dezhnyov reached the mouth of the Anadyr River and sailed up it in 1649, having built new boats from the wreckage. They founded Anadyrsk and were stranded there, until Stadukhin found them, coming from Kolyma by land. Subsequetly Stadukhin set off south in 1651 and discovered Penzhin Bay on the northern coast of the Okhotsk Sea. He also may have explored the western shores of Kamchatka.
In 1649–50 Yerofey Khabarov became the second Russian to explore the Amur River. Through Olyokma, Tungur and Shilka Rivers he reached Amur (Dauria), returned to Yakutsk and then back to Amur with a larger force in 1650–53. This time he was met with armed resistance. He built winter quarters at Albazin, then sailed down Amur and found Achansk, which preceded the present-day Khabarovsk, defeating or evading large armies of Daurian Manchu Chinese and Koreans on his way. He charted the Amur in his Draft of the Amur river. Subsequently Russians held on to the Amur Region until 1689, when by the Treaty of Nerchinsk this land was assigned to Chinese Empire (it was returned, however, by the Treaty of Aigun in 1858).
In 1659–65 Kurbat Ivanov was the next head of Anadyrsky ostrog after Semyon Dezhnyov. In 1660 he sailed from Anadyr Bay to Cape Dezhnyov. Atop his earlier pioneering charts, Ivanov is credited with creation of the early map of Chukotka and Bering Strait, which was the first to show on paper (very schematically) the yet undiscovered Wrangel Island, both Diomede Islands and Alaska, based on the data collected from the natives of Chukotka.
So, by the mid-17th century Russians established the borders of their country close to modern ones, and explored almost the whole of Siberia, except the eastern Kamchatka and some regions north of the Arctic Circle. The conquest of Kamchatka later would be achieved in the early 1700-s by Vladimir Atlasov, while the discovery of the Arctic coastline and Alaska would be completed by the Great Northern Expedition in 1733–1743.