Thresholds in asset accumulation dynamics can drive a wedge between households able to pursue relatively high-return, asset-based economic activities and those forced into lower return alternatives. While some evidence has been found for such thresholds amongst pastoralist communities in the arid and semi-arid rangelands of northern Kenya, relatively less is known about the mechanisms behind such poverty trap phenomena. The setting is particularly suitable for such a study because there is one primary high-return livelihood, mobile pastoralism, based on a scalar primary asset stock, livestock. Sustainable pastoralism involves livestock movements in response to the bimodal rainfall distribution. I develop and provide empirical tests for the implications of a simple model capturing the idea that the bifurcation in asset dynamics is driven by a threshold in the incentive to engage in mobile pastoralism. Additional evidence is presented regarding pastoralist movement patterns. Data collected on pastoralist concerns allows us to look at the effect of subjective beliefs on subsequent mobility and movement behavior.