Why do young landscapes sometimes have few well-developed valleys?

In the context of the geomorphic cycle, young landscapes—often characterized as being in the "youthful" stage of development—typically feature broad, undissected divides and narrow, deep valleys.12

The relative lack of well-developed, broad valleys in these landscapes is primarily due to the stage of erosion and the nature of fluvial processes following initial uplift. During this early phase, rivers expend the majority of their energy in vertical entrenchment rather than lateral erosion. Because the streams are focused on cutting downward to reach a baselevel, they create narrow, steep-sided forms like canyons or gorges rather than the wider, more mature valley floors seen in later stages of landscape evolution.314

As denudation continues over time, rivers eventually smooth out their longitudinal profiles and shift their energy toward lateral erosion, which progressively broadens the valley floor. Consequently, the presence of narrow valleys in a young landscape is a direct reflection of the early, vertical-dominant phase of river incision.31