The islands have an aggregate area of 244.97 km². 1,116 people lived on Isla María Madre as of the census of 2005 along with around 8,000 prisoners. The other islands are uninhabited. The main settlement is Puerto Balleto, with a population of 602. Isla María Madre is the largest of the islands, with a surface area of 145.28 km². It houses the Islas Marías Federal Prison, which was established there in 1905. The next two largest islands are Isla María Magdalena and, further south, Isla María Cleofas. They were named after three women called Mary in the Biblical New Testament: respectively, Mary, the mother of Jesus, Mary Magdalene, and Mary, the wife of Cleopas, and are referred to as the Tres Marias. A smaller island, San Juanito, with an area of 9.1 km² lies off the north coast of Isla María Madre. The islands are listed from north to south in the following table:
Island or Rock
Area km²
Height m
Location
San Juanito
9.105
.
Piedra El Morro
0.060
.
María Madre
145.282
616
Isla Don Boni
0.025
.
María Magdalena
70.440
457
María Cleofas
19.818
402
Piedra Blanca
0.172
.
Roca Blanca
0.034
.
unnamed rock
0.034
.
Islas Marías
244.970
616
Geology
Research supports the hypothesis that the Islas Marias are fragments of continental crust left over from the separation of the Baja California Peninsula from the mainland of Mexico. Rocks found on the islands correspond with rocks found around Cabo San Lucas, as well as Puerto Vallarta.
Populated places
All populated places of the Islas Marías are on Isla María Madre. They are listed from north to south in the following table: Each populated center features a different economic activity. The primary population center is Puerto Balleto, the location of the administrative offices and the primary centers of commerce and recreation. It is subdivided into four jefaturas:
The mean temperature of island remain between 84 and 89 degrees Fahrenheit throughout the year. In April, May, and June sometimes temperatures cross the limit of thirty-five degrees Celsius. In December, January, and February the temperatures remain under twenty-five degrees. Sometimes the temperature may drop under twenty degrees Celsius. Most of the time weather remains dry but July, August, and September may receive rain up to 10mm. The average wind speed is between twelve and nineteen km/hour. The below chart shows the maximum and minimum temperature.
Unit
Celsius
Celsius
Celsius
Celsius
Celsius
Celsius
Celsius
Celsius
Celsius
Celsius
Celsius
Celsius
Mean
Daily Max
29
29
31
32
34
34
32
31
31
31
31
29
Mean
Daily Min
13
14
15
17
19
22
24
24
24
22
18
15
Month
Jan
Fab
March
April
May
June
July
August
September
October
November
December
Hurricane Willa
passed through the Islas Marias on October 23, 2018. The National Hurricane Center reported at 9 AM MDT "Aircraft finds the core of Willa passing over Las Islas Marias Mexico". A subsequent report from the NHC stated that "Life-threatening storm surge is occurring along the coasts of the Isla Marias'. The NHC also reported that "An automated observing site on Las Islas Marias recently reported a sustained wind of 88 mph with a gust to 112mph ".
Lighthouse
There is a lighthouse located on a ridge above Puerto Balleto on Isla María Madre. The height of tower is two hundred feet or sixty-two meters. The lighthouse main gallery is painted white while the tower of the lighthouse is colored in red and white. The lighthouse is made of concrete and a large single story keeper house is also constructed with the lighthouse. The light house shines two white flashes every 10 seconds. The diameter of the light house is seven meters.
Prison of Isla Maria
The Islas Marías Federal Prison was constructed in 1905. One of its more notable prisoners was the Mexican progressive writer Jose Revueltas who wrote his first book Los Muros de Agua while incarcerated there. Mexico's newly-elected president Andres Manuel Lopez Obrador announced on February 18, 2019 that his administration will close the Islas Marías Federal Prison, replacing it with a new cultural center that will be named for Jose Revueltas.