The John Muir Trail. Alan Castle

      Mount Lyell, the highest peak in Yosemite, with its small glacier, towering above the head of Lyell Canyon (Day 5)

      If you travel from south to north, beginning at Whitney Portal, there are four major disadvantages. The very first stage is a climb of over 6000ft to the summit of Mount Whitney, at the seriously high altitude of 14,496ft. At this stage you will not be altitude acclimatised and so run a serious risk of suffering altitude sickness, which at best would severely affect your ability to continue northwards along the JMT. Secondly, there is no point along the route of the JMT between Whitney Portal and Muir Trail Ranch where further food supplies may be picked up, so the poorly acclimatised and unfit trail hiker would have to begin the walk by carrying a heavy load of 10 days’ worth of food from the very beginning of the trek. Thirdly, the southern half of the JMT passes through areas of total backcountry wilderness, where escape routes are relatively few and far apart (a list of escape routes is given in Appendix 3), and where even these usually require at least two and often more days to reach civilisation. So the most serious part of the Trail is encountered at the beginning of the trip when the overseas walker will be unused to the American wilderness and so less able to cope. Lastly, the southern section contains a half-dozen high mountain passes of over 10,000ft which come in quick succession, almost one per day. Again the walker not yet trail fit and altitude acclimatised will find the crossing of these high cols extremely arduous.

      By walking from north to south, Yosemite to Whitney, all of these problems are overcome. The northern end of the Trail is at a much lower altitude than the southern half; compare the summit of Half Dome, 8836ft, with those of the 11,000ft+ passes further south and the 14,496ft of Mount Whitney itself. The climbs in the northern half of the Trail are generally not as long and hard as those further south, and altitude is gradually gained as the walker heads south, so allowing good acclimatisation. Furthermore, just three days (or even only two days if Half Dome is omitted) after leaving Yosemite Valley, Tuolumne Meadows on a main road is reached, where food supplies may be picked up and prepared foods purchased. Three and a half days later Reds Meadow is encountered, with similar facilities. Then, 2½ days after that, comes the comfort and hospitality of Vermilion. And only two days later comes Muir Trail Ranch, which allows pre-posted food packages (see ‘Posting food on ahead’, below) to be collected. So there is less of a wilderness aspect on the northern half of the JMT compared to the southern half; the walker can therefore build up his or her trail fitness and experience of the Californian wilderness before tackling the harder, higher, wilder sections in the south.

      For all these reasons the JMT hiker is strongly recommended to walk the Trail north to south, from Yosemite to Whitney. This is the direction described in this guidebook.

      Shorter Routes Include:

      When to go

      The JMT is a high-level route over the High Sierras, mostly above 9000ft in altitude and often above 11,000ft. Very considerable quantities of snow fall on these mountains during the winter months. Snow remains on the high passes usually well into early summer. July is the first month of the year when the JMT could sensibly be considered, but in years of late spring snows it is likely that the higher sections of the Trail will still have a covering of snow, at least in the early days of that month. Melting snow also means swollen rivers, so an early summer crossing increases the risk of encountering difficult and dangerous river crossings.

      The recommended month to hike the JMT is August, when the risk of lying snow and rivers in spate is at its lowest. Mosquitoes, which can be a menace in some areas, tend to be less of a nuisance later in the summer. The temperature even at the high altitudes of the High Sierras will probably be fairly high at this time of year (at least in the high 20s Celcius and probably well into the 30s), with some low temperatures at night (often at or below freezing), but with relatively low risk of severely low night-time temperatures. Precipitation, either rain or snow, will probably be very low. However, violent thunderstorms with heavy rain, snow and hail can occur even during the summer months. This mountain range has one of the best climates of any high mountain area in the world, and most days during the summer months have blue skies and wall-to-wall sunshine.

      The first week of September is also acceptable, but by mid-September some of the resorts and other facilities en route may be closing down, particularly if the weather starts deteriorating. However, September does have several advantages for experienced backpackers, including few mosquitoes, less traffic on the trail, ease of obtaining permits, autumn colours and fewer thunderstorms, but at the risk of freezing nights, a higher probability of snow and the stores (Reds Meadow and Vermilion) en route running down stock for the close of the season. By the end of September night-time temperatures are likely to plummet significantly, with the first heavy snows of the season at high altitude a very real possibility. By early October all the facilities on the JMT are closed, as winter begins to creep slowly into the High Sierras.

      All or part of the trail?

      Overseas walkers are likely to spend a considerable sum of money travelling to the western United States and to invest a fair amount of time in planning the hike; they often wish, therefore, to attempt the whole of the JMT. However, with time for food provisioning and other preparations, and travel to and from the trailheads, plus time for sightseeing in San Francisco and elsewhere, the total amount of time required to walk the whole of the JMT is at least four weeks.