From the confluence of the river Moyobamba to the point by which the mountainous territory is terminated, the Huallaga throws off four branches, which form as many different passes, named Estera, Canoayaco, Chumia, and Yuracyaco. At the point where if disembogues itself, it flows gently, taking a declination to the north, through an immense and fertile territory, which it overflows to the extent of three or four miles in breadth. Pursuing its course by the province of los Maynas, in 5 degrees 4 minutes south latitude, it falls in with the Maranon, by which, divided into two branches, it is received. At the junction a gulf is formed half a league in breadth, and 28 fathoms in depth. The diagonal line which results from the confluence of the two rivers, follows a space of about a league without either of them having a preponderance over the other. At length the direction of the Maranon overcomes that of the Huallaga.
Father Manuel Sobreviela, with a view to explore the navigation of the latter of these two rivers, sailed from the college of Ocopa on the 1st of July 1790, and, proceeding by Tarma and Pasco, reached, on the 7th, the pleasant city of Leon de Huanuco, distant from the above college fifty-six leagues. From Huanuco it was his intention to direct his steps to the new town of Playa-Grande, situated on the banks of the river Patayrrondos, where it is customary to embark in descending that river as far as its confluence with the Monson, distant half a league. Having embarked on the latter river, he was to proceed to the Huallaga, distant four leagues from the above-mentioned confluence. The passage overland, however, from the city of Huanuco to Playa-Grande, a distance of thirty leagues, being rendered in a manner impracticable by the difficulties which a rugged mountain opposed, it became necessary to remove these obstacles before the expedition could proceed. In the year 1787 the reverend father had begun to open a road which might facilitate the passage by mules over this mountain. To complete this undertaking, he sent notice to the governor of Panataguas, and to the sub-delegate of the province, that, in virtue of the directions of the intendant of Tarma, Don Juan Maria de Galves, they were to furnish, without delay, the succours and people
- In this part, as well as nearly throughout its whole extent, the Huallaga was found to have a breadth of 180 fathoms, and a depth of 28. It was measured with great exactitude by father Sobreviela, aided by the lieutenant-governor of Maynas, Don Juan Salinas, a man of conspicuous talents, who was very solicitous to promote, by his personal exertions, the success of the peregrinations we are now describing. The breadth of this river was computed by M. Condamine at 250 toises, at the same season of the year; but as his measurement was made by the eye, that of father Sobreviela and Don Juan Salinas ought certainly to be preferred.