At least 257 people were forced to abandon 90 homes in Tijuana, Baja California, due to landslides on Monday.

In the rugged, hilly terrain of the Camino Verde neighborhood, 172 adults and 85 children from some 100 families saw their homes collapse when cracks opened in the ground.

Local Civil Protection officials found visible structural damage to the homes and decided to evacuate residents. A further 50 houses were categorized as being at risk, and at least 40 properties over an area of four blocks were recorded as having non-visible structural damage.

Local authorities cut off the water supply to the area without prior warning, much to the irritation of those who hadn’t abandoned their homes, the newspaper Milenio reported. The electricity supply was also cut, the newspaper Excélsior reported.

A resident of the neighborhood who gave his name as Francisco said water leaks were to blame.

“There were various leaks from the upper part that we have just been inspecting,” he said before showing cracks in the walls of houses, the streets and pavement.

Tijuana official Jorge Salazar Miramontes said that a sports center had been turned into a shelter for the affected families.

Tijuana’s College of Civil Engineers (CICTAC) will investigate what caused the incident. “Geotechnical studies report on the properties of the soil and how the layers of subsoil are formed,” CICTAC President Gerardo Tenorio Escárcega explained. “Geophysical studies show you the weaknesses, holes [and] cracks and also determine the moisture content of the soil.”

Housing developments in elevated parts of the city have been built over streams, and the lack of natural drainage makes those areas vulnerable to landslides, but it is not clear if that was the case for the Camino Verde neighborhood. Heavy rains and flooding can provoke shifting earth and landslides, as can earthquakes.

Tijuana is located in the Imperial Fault Zone, which encompasses most of southern California and makes Tijuana vulnerable to quakes.

The problem of landslides and dangerously shifting soil goes back years in the city, with multiple incidents in various neighborhoods that have forced people to evacuate their homes. In 2015, after a landslide provoked by a water leak forced 19 homes to be evacuated in the Anexa Miramar neighborhood and left 21 more buildings at risk, Baja California’s Civil Protection agency called the risk of landslides and shifting earth “an old and serious problem,” blaming, among other factors, Tijuana’s history of irregular and “abusive” construction of developments on uneven land with soil layers that are not well compacted and that vary in their permeability.

With reports from Excélsior, Milenio and El Sol de Tijuana