If it isn't due to lactic acid build up, then increasing calcium uptake won't help. Calcium and other electrolytes are used to control pH levels in the cell, maintaining an optimum environment for cellular respiration and other processes. When aerobic cellular respiration slows (which can be due to many factors; lack of water, lack of oxygen, improper cellular pH inhibiting respiration specific enzymes), the cell will switch over to anaerobic respiration, which produces lactic acid as a byproduct and will eventually lead to cell death.

If the cramps are due to some neurological disfunction, increasing sodium and potassium intake might help. In general, and without a specific diagnosis as to the cause, it'd be best to increase both water and electrolyte intake, and maybe take it easy for a couple of days to let your body replenish it's levels.

It's funny that you cramp on long hikes up; I never cramp hiking up, but instead have an issue with long hikes down. The only times that I cramp cycling are during sprints after long periods of sustained exercise, basically overtaxing my muscles.