CASTRO VALLEY -- Authorities are investigating two suspicious brush fires that broke out Wednesday night in less than an hour and only a few blocks apart.

Fire crews were dispatched just before 6 p.m. to the area of Walnut and Almond roads for a report a grass fire, said Alameda County Fire spokeswoman Aisha Knowles. Crews arrived and were able to quickly get the blaze under control.

Less than one hour later, at 6:48 p.m., crews were called down the street to the 17000 block of Almond Road for a report of a house fire, Knowles said.

But when crews arrived, they did not find a home on fire. Instead, they located a brush fire, which they also put out.

Investigators on Thursday said foul play was suspected in both fires.

Neither the cause of the fires nor their origin were immediately known Thursday, and they both remained under investigation, Knowles said.

Anyone with information about the fires is asked to call the Alameda County Sheriff's Office at 510-667-7721 or an anonymous tip line at 510-667-3622.

Contact Natalie Neysa Alund at 510-293-2469. Follow her at Twitter.com/nataliealund.