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The Pear Lake basin (36°36'02"N, 118°40'00"W) is located in Sequoia National Park about 1 km northeast of Emerald Lake. Monitoring began in 1986. Pear Lake is relatively large and deep compared to other lakes. The lake has a maximum depth of 27 m, a mean depth of 7.4 m and volume of 591,000 m3. Because of its depth, thermal stratification is strong during much of the year and low dissolved oxygen concentrations occur in the hypolimnion. Mixing of the lake occurred during the spring and autumn but appeared to be incomplete; water temperatures at a depth of 25 meters rarely exceed 5°C. As a consequence, redox potentials are low in the hypolimnion as evidenced by low pH and the accumulation of hydrogen sulfide, ammonium, and iron in these waters.

The outlet to Pear Lake is at 2,904 m and the vertical relief of the basin is 471 m. Owing to the large volume of the lake, the V/A index is high (0.45 m) relative to the other acid rain study lakes indicating that Pear Lake has a greater influence on outflow discharge and chemistry. The lake is fed by one major inlet stream during most of the year, but probably receives a significant portion of snowmelt from sheet flow off of extensive areas of exposed bedrock surrounding the lake. The outlet typically flows year round, but can dry up when snowfall is low and non-winter precipitation light (e.g., water year 1990).

Most of the Pear Lake watershed is composed of coarse-grained granites containing sparse mafic inclusions of widely variable size and texture. The remainder of the basin is underlain by medium-grained, porphyritic granodiorite. Greater than 90% of the catchment is composed of bedrock, talus and boulders. What little vegetation is found in the basin consists of a few stands of coniferous trees (Lodgepole Pine, Western White Pine, Red Fir), shrubs, grasses and sedges. Soils, where present, are classified as Alpine Brown.