Although NY 70 is mostly signed north–south, it follows a more southeast–northwest alignment and is considered an east–west route by the New York State Department of Transportation (NYSDOT).

[3] As such, the route officially begins at an intersection with NY 436 in the town of Portage, located in southwestern Livingston County.

[1] It initially heads southward across open fields and past small wooded areas before curving to the east about 1 mile (1.6 km) later.

[3] From Dalton southeast to Canaseraga, NY 70 closely parallels the Norfolk Southern Railway's Southern Tier Line as both the road and the rail line run along the base of a valley surrounding Canaseraga Creek, the source of which is located roughly 3 miles (5 km) east of Dalton.

The valley takes the route and the railroad southeastward into Allegany County, where they both pass through the towns of Grove and Burns.

East of Garwoods, the creek curves to follow a more easterly track, and the valley, NY 70, and the Southern Tier Line all turn eastward to match the change in course.

Just over 2 miles (3.2 km) from Garwoods is the creekside village of Canaseraga, a stark departure from the isolated, undeveloped areas that NY 70 serves west of this point.

At this point, the Southern Tier Line heads south to follow NY 961F toward Hornell and Canaseraga Creek turns north toward the Livingston County village of Dansville.

The first was made c. 1974 when the route was truncated westward to Arkport following the completion of the Southern Tier Expressway between Hornell and Avoca.