The North Sister is oldest, with towering rock pinnacles and brilliant glaciers. It has not erupted since the late Pleistocene. It is the most dangerous climb of the Three Sisters, due to its level of erosion, and thus rockfall.

The Middle Sister is the smallest and most poorly studied. It is the second youngest. No reports on its potential for eruptions can be made.

The South Sister is the youngest and tallest volcano of the trio. It last erupted about 1600 years ago. It has a well developed crater, which is covered by a glaciated lake. It is a long, steep, non-technical hike that can be easily completed in a day by reasonably-fit hikers. Popular starting points are the Green Lakes or Devil's Lake trailheads.

In 2000, a satellite discovered that there was a deforming uplift near the South Sister. This could mean that she is awakening. Depending on the type, the eruption could either result in quiet emissions of lava, of the town being buried, or even a total levelling of the mountain.

The Sisters were named Faith, Hope, and Charity by early settlers.

In a technique known as companion planting, the three crops are planted close together:

1. build flat-topped mounds of soil for each "cluster", about a foot high and 20 inches wide
2. plant several corn seeds close together, in the very center
3. when the corn is 6 inches tall, plant beans and squash around the corn, alternating between beans and squash

• The corn provides a structure for the beans to climb, eliminating the need for poles
• The beans provide the nitrogen to the soil that the other plants remove
• The squash spreads along the ground, monopolizing the sunlight to prevent weeds
• The squash also acts as a "living mulch," creating a microclimate to retain moisture in the soil

"Three Sisters" is a variety of tomato, so named because the plant grows fruit in three different shapes