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The Preguda Boulder

Italia, Regione Lombardia, provincia di Lecco, Malgrate

Positioning

Sasso di Preguda

COORDINATES
(CH 1903) E   749190 N   80968 H   615.0
(WGS 84) Long.   9.360 Lat.   45.864
GENERAL EVALUATION
DIFFICULTY E-T2/T3
SCIENTIFIC INTEREST PRIMARY:
Glacial morphology

SECONDARY:
OTHER INTERESTS Ethnographical, Landscape
Hiking, Historical
GEOSITE   GEOMORPHOLOGICAL - glaciers

DESCRIPTION

The Preguda Boulder is an erratic block of gigantic dimensions, composed of ghiandone granite, a coarse-grained biotite granite of the Carboniferous Period. It was deposited by the Abduano Glacier on a natural rock balcony overlooking the Lecco branch of Como Lake. Set against the rock is a chapel dedicated to Saint Isidoro. From this vantage point there is a broad view of the eastern shore of the Lecco branch and the massif of the Grigne group. A plaque affixed to the rock celebrates the famous abbot Antonio Stoppani (1824 - 1891) to whom we owe the first geological and geomorphological studies of the Como region.

INSIGHT

The Preguda Boulder is comprised of a type of granodiorite, a plutonic igneous rock, called “ghiandone”, whose name is derived from the appearance of large crystals of potassium feldspars (orthoclase), of a form roughly similar to that of acorns. The “ghiandone” emerges extensively in upper Valtellina and was transported there by glaciers which descended the mountain valleys to the south several times during the Quaternary Period. The path to the Preguda Boulder is also punctuated by the presence of several other erratic boulders, located at lower altitudes.

CURIOSITIES

Along the way you can see many buildings contructed of dry stone in a roughly circular layout locally known as “Casotte”. The ceiling may either be arched or pointed, and is usually covered with earth. Some of these buildings have recently been restored by the local community, though it is still possible to see others in their original condition. They are small huts of an ancient tradition, probably used as shelters for shepherds and local farmers. In the mountainous areas of Valmadrera there are more than 500 of these huts, some in excellent condition, while others are completely in ruins.
scala temporale periodi geologici

HOW TO REACH THE SITE

Coming from Milan on the S.S. 36 motorway, take the exit for Valmadrera. Follow Via Roma and then continue on Via Preguda. After a short descent, turn left towards Piazza Rossè and go uphill to the parking area.

USEFUL INFORMATION FOR THE VISIT

Trail number 6 leads to a convenient mule track which climbs up the sides of the south-eastern slope of Moregallo. You will reach the Preguda Boulder in about an hour.

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Programma di cooperazione transfrontaliera Italia - Svizzera 2007 - 2013 Progetto cofinanziato dal Fondo Europeo Sviluppo Regionale (FESR)
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